Noise reduction program (sound insulation DIY)

[xtp77]

While overall super happy with my 2.0TDI, I hear too much the engine noise. It is not the end of the world, but it grinds me down on long journeys. And particularly when I compare with the Volvo S60 I used to drive. So I started researching how to make it quieter. This post is documenting what I have done and I will do. And in case anyone has ideas, just add to it.

 

1.- Ideas to get references:

• The superb III owners has a very long thread (23 pages and counting) on the topic. It made me wonder that maybe the mk2 is better in this regard.
•  This YT channel has interesting material. Example video: Sound Deadening a Car Where It Actually Makes a Difference!
• A bit off topic, but this video How Much Weight can you REMOVE from your Car? (Weight Reduction) opened my eye to the insane amount of insulation material you can find in a BMW 3-series. I do suspect you won't find the same in a Skoda.
• Insonorizar Coche a Nivel Profesional | El Secreto de los Coches de Lujo. What would it take to go full in into making a car quiet (in Spanish)

 

2.- My plan. So I won't go a fully deep as the pro-video at the end (though I may consider it), but I do plan on making the 20% that may give 50% of the return. Bonnet insulation, trunk insulation, and a quick change in the floor mats.

 

3.- Progress so far:

 

ACTION 1: In the trunk, I put sound absorption under the spare wheel. There is very little sound dampening, but I made a quick fix. I got approx 1x1m sound absorbing foam, made a hole, and threw it under the wheel. 

 

This was super quick to do, and about 14 EUR for the foam, if I recall correctly.

 

RESULT: My goal is mainly to reduce engine noise, so it had no impact there. But this was super quick and easy. Interestingly, the back feels way quieter. Right after doing it, I game me the impression that a chunk of the car in the back was missing, because I didn't hear as much noise.

 

RECOMMENDATION?: Yes do it, because it is super fast. Also, it can be undone, there is no glue involved.

 

Picture of the kind of material I am taling about.

Picture of the wheel space BEFORE I put the foam. I have no after pictures, but basically anywhere you see metal sheet (brown), now is covered with foam.

 

 

ACTION 2: INJECTOR CLEANER. I read it may help the enginge run better and be smooother. I had to do it for maintenance regardless.

 

RESULT: No difference in sound.

 

RECOMMENDATION? For the injectors, and also it is quick and cheap. But no noise change at all.

 

ACTION 3: NEW CARPETS, AND STICKING NOISE ABSORPTIONUNDERNEATH. So I got new mats, because the previous ones were too old. These are rubber, as they fit better how I use the car. Happy with the mat, and decided to stick a 1cm thick sound foam underneath. It took me some time to cut it to size.

 

RESULT: Less vibration through the feet. A bit less of noise probably.

 

RECOMMENDATION? Optional, but I do appreciate a bit less of vibration. Also, super easy place to add noise insulation on the interior, as one has perfect access.

 

 

 

 

 

ACTION 4:  CAR BONNET 1. ALUBUTYL LAYER

 

So now heading straigth to address my main problem with engine noise. This requires a bit more time, and I am still working on it. First, I removed the headshield in the car...

 

and there is the heat shield, that starts to show its age (14 years), not looking flexible and letting go some powder. Also, the bonnet metal sheet has zero sound dampening or insulation. I don't know if the heat shield is supposed to absorb noise, but I do not think it is in any condition to do so effectively.

 

So yesterday, I started to apply alubutyl layer, and sticking it. I am only 40% done, because I ran out of time and the surface is complicated with all the different crevices. This is a bit of a tiresome job.

 

RESULT: So far, inconclusive. I can't sense a difference. but I am not done....

 

FUTURE ACTIONS:

• ACTION 4:  CAR BONNET 1. ALUBUTYL LAYER, COMPLETE IT. Maybe in a couple of weeekends I will have time, and then...
• ACTION 5:  CAR BONNET 2. SOUND INSULATION LAYER. I will add a second layer of sound insulation foam. From the videos, alubutyl mainly prevents vibration on the metal, and the job of the sound foam is to absorb the noise. So both work together better. I will report back with pictures on both processes.
• ACTION 6 - MAYBE: Figure out where else in the engine bay can alubutyl and sound insulation be applied.
• ACTION 7 - MAYBE: Put noise absortion in the front wheel wells.

 

UNLIKELY ACTIONS:

• I won't go any deeper on a DIY mode (no door panels, removing seats and carpet, dismounting pillars,...)
• If I am not satisfied, I may go to get a professional sound insulation, the kind that
  • removes the seats
  • removes carpet
  • removes car panels
  • ...and adds insulating material throughout. Like the Spanish video I link above.
• Any ideas on cost?
• If I am not satisfied, make peace with it. Or save a lot of money and buy a Lexus.

 

 

That is my plan. Any ideas, welcome! I will report back as I make progress.

 

[xtp77]

Adding a bit of detail on the carpet insulation.

 

The underside of the carpet before applying the insulation:

 

After applying the noise insulation:

 

And the topside is exactly as it was before, so nothing to see:

 

And then it fits into place nicely.

[bigjohn]

Generally I find my mkII incredibly quiet but mine is the poverty spec with quieter higher profile Crossclimate tyres and of course it's a petrol.

 

Back in the day when I made a kit car I found the most effective but less intrusive way of sound proofing was bitumen sheets applied to front and rear bulkheads, transmission tunnel, floors, foot wells etc. The sheets were quite thin so didn't intrude re carpets etc. As well as the noise reduction it eliminated body panel resonance - almost made it toooo quiet for a sports car.

 

Be careful under the bonnet re flammable materials etc.

 

Edited 5 March by bigjohn

[xtp77]

 

Diesel vs petrol makes a huge difference indeed.

 

On 05/03/2024 at 14:21, bigjohn said:

the most effective but less intrusive way of sound proofing was bitumen sheets applied to front and rear bulkheads, transmission tunnel, floors, foot wells etc. The sheets were quite thin so didn't intrude re carpets etc.

 

 

Thanks for the suggestion. I would like to go down that route, but I don't want to DIY removing the carpet and getting to the metal. I don't think I can pull it off. Well, maybe I can pull the carpet off, but not put it back on properly with all the seats and connectors and damaging nothing. It is easier when you build it from scratch   If I don't get enough noise reduction, I may ask for an audio-car shop to do it for me.

 

And your call out on flammable materials is very valid. I am checking for operating temperatures of the material, and so far it should be good. Last thing  I want is a really quiet bonfire of a car!

 

[xtp77]

Continuing today, with the layer of Alubutyl

 

ACTION 4:  CAR BONNET 1. ALUBUTYL LAYER

 

So I did most of the layer. It is a complicated material, because of how it has to be applied. Super important to (a) clean the surface well with alcohol and (b) get a roller, in order to make the right pressure. If the rubber doesn't glue well with the metal, it will not dampen the vibration. 

 

Also, there are no big surfaces in the bonet, as it has this "double layer  structure", with a sun-like, or spider-like in the middle, which makes it difficult to apply the material. I made multiple cuts of material and applied it with the roller.

 

RESULT: Noticeable less vibration from the engine, but not as effective as I expected it. But I found the noise less intrusive than before. The noise was less droning, which is exactly what I am goinf after. 

 

RECOMMENDED? Yes, because it is still an easy access area and the vibration is less.

 

Next step will be to put in sound absorbing foam and see how it works together.

 

Below: Picture of the alubutyl as I was halfway done with the process.

 

 

 

[mbgar]

Interesting topic

 

Did you put the foam sound absorption mat under the spare tire  or did you simply put a somewhat rectangular piece on top of it between the trunk cover and tire?

 

After applying the alubutyl onto the hood how heavy became the hood?

Is the hood lifter still sufficient? Is there enough left so you can mount the original mat back again onto the hood covering the alubutyl?

How much squaremeters Alubutyl would you estimate you need for the engine hood?

Edited 16 March by mbgar

[mbgar]

@xtp77

 

And another question since I cannot edit anymore:

Is alubutyl a good choice for deadening the engine hood or would neoprene be better?

Both have roughtly the same temperature range, but neoprene is much lighter

[xtp77]

I find it very interesting. I was wondering whether the car has become noisier with age, due to more rattling and aged sound absorbing materials, or I have become pickier. Maybe both.  

 

To your questions:

 

1. I put the foam under the spare tire. I figured it would be kept in place and absorb vibration directly. Plus no hassle if I ever need to use the tyre.  I will try to upload picture later. 
2. I have added approx 1 sq meter of alubutyl, which is 3kg approx. The weight distribution matters, I put more densely the material close to the cabin, where it creates less leverage, and less farther away. I also thought I wanted more material close to the cabin
3. Lift holds the bonnnet without issues. However, no idea how close to the limit of extra weight this is. 
4. Even before, one has to lift the bonnet a bit to open it, and now it is a bit heavier. 
5. The heat shield covers all alubutyl. The shape matches the rubber seal along the engine bay. I have doubt's on whether material beyond that shape would effect the noise level at all
6. The heat shield is, and will remain in place. With the alubutyl, as it is only 2mm thick, there is no problem.
7. Once I have the sound reduction foam, I need to be more careful as it is 10mm thick. I reckon that 10mm extra thickness will not allow the clips holding the heatshield to hook properly. So at least around the clips, no foam. I will have to figure that one out. 

 

[xtp77]

This picture shows what I did in the spare wheel. As my main focus is diesel engine noise, this was really quick DIY. Maybe in the future, I will do a second passing. 

 

[xtp77]

5 minutes ago, mbgar said:

@xtp77

 

 

Is alubutyl a good choice for deadening the engine hood or would neoprene be better?

Both have roughtly the same temperature range, but neoprene is much lighter

 

I don't know.

 

What I know: I will put a layer of alubutyl and one of sound absorbing foam on top of it. The first prevents the hood from rattling, creating and amplifying noise like a speaker or a guitar body. To do so, it has to be well glued to the metal sheet.  The latter to absorb as much noise as possible. 

 

I am unclear on whether neoprene would be similar to either one. Also, I mainly saw those on Amazon, I don't recall neoprene. Or maybe it goes with another name. 

[xtp77]

I am done with the project. Final notes:

 

ACTION 5:  CAR BONNET 2. SOUND INSULATION LAYER. 

 

After completing the alubutyl layer, I placed a layer of sound aborbing foam.  The material is superlightweight, specially compared to the alubutyl. So no impact whatsover in the lifts.

 

Things to keep in mind:

• Challenge 1: Because the bonnet structure is "like a spider with a sun in the middle", it was difficult to place a continuous layer of foam, so I had to do multiple cuts. It doesn't lok pretty, but there is a layer of foam in most of the bonnet.
• Challenge 2: The material is thick, about 10mm, so it is important to leave areas without materials close to the clips that keep the heatshield in place. The clips still hold, but some were strained.
• Challenge 3: There are areas between the two layers of metal that are hard to reach. I still put material, because I had leftover and it is lightweight.
• Challenge 4: The adhesive can stick while one is trying to position the foam piece, so need to be careful.

 

A couple of pictures to illustrate.

 

Picture 1: The bonnet with the alubutyl layer BEFORE applying the foam. Underneath the outer sheet of metal, there is a circle in the middle, then an outer circle, and six beams of metal that are on a different plane. Pllus other irregularities. This makes the application complicated. 

 

Picture 2: The finished product. Notice that some of the "metal rays" have no foam on  top, because that would prevent the clips from holding the heatshield in place. Also, it has so many cuts and small pieces, it was very difficult to apply a single continuous phase. Still, I'd say that there is 90% coverage of the surface. Often there is foam underneath the metal sheet that can be seen in the picture. Both in the beams, but also underneath the margins.

 

Picture 3: Final state with the heat shield back on. I placed a but of alubutyl beyond it, but I don't think it matters much.

 

 

So, after all of the effort, was it worth it? I will do a summary post right below. 

 

[xtp77]

Overall summary: Definitely worth the effort, clear improvement, far from perfect. And this car will always be a noisy Diesel.

 

In more detail: 

 

Effort: The  above work took me about 2-3h of work (albeit split in mini sessions, waiting for materials to be delivered, etc...), and a total cost of 100 EUR. Very reasonable.

 

Result: Measuring the car, here are the noise levels (no music, no AC) I measured with an app after doing all of the above, on average:

• 42dB Cold engine idling 
• 33dB Warm engine idling (surprising reduction of noise!)
• 55dB climbing a steep hill at 60km/h, cold-ish engine
• 62dB 130km/h highway, mild climb

Frankly, I have no idea what the above numbers mean, and also who knows whether an app on my phone is a well calibrated device, most likely not.

 

With hindsight, a before and after measure in a controlled area of road would have been a better way to measure. 

 

So maybe the more important is...

 

Perception - Positive: Very interesting! I do perceive less noise in the car. But as this has been a somewhat long process, due to waiting for materials, I think I got used to it. It is easier to talk inside the car, the reduction on noise from the back was very noticeable after the foam layer, and now after the final foam I also sense a drop in the engine noise, which is the most important.

 

The best way to describe how I percieve the change is this: the engine noise is the same, but it feels like the engine is located further away. Like instead of being in front of me, the engine is located five or 10m in front of me.

 

To describe the effect, the analogy that comes to mind is that the "before state" felt like like having a neighbour doing some noisy renovation. And then the "after state" is like the renovation has moved two or three houses down the road. It is still the same nature of noise, it may still be annoying or distracting, but it is much more muted. Which brings me to...

 

Perception - Neutral/Annoying: Two things haven't changed, and those make the result not as good as I expected.

 

1. Vibrations. The level of vibrations that comes from the engine into the cabin has not changed. The kind of vibration one can feel in the heel, in the pedal, or when resting the leg on the side. Those vibrations remain the same before and after and affect comfort. This car would not pass the Lexus Champagne Glasses Balance At 145 mph

 

2. Diesel sound. The nature of diesel noise is more annoying vs gasoline. The noise is more irregular, coarse, definitely not smooth, thus perceived as noisier and more annoying, and the vibrations are higher because of the compression ratio. Here is a good explanation: Why Diesels Are So Loud? Why Are Diesel Engines So Noisy?. And, of course, the nature of the diesel sound doesn't change with my DIY project. And even if I went 10x on noise insulation, the nature of the noise would remain annoying, less precise. 

 

So my perception of the engine noise and vibrations is definitely still there, just more muffled. Which is good, but definitely not perfect.

 

For the final round of FAQs:

• Would I recommend doing it? Yes, simple nice little DIY project that does reduce the noise.
• Will I do more noise dampening?  No, this is enough. I will not do more DIY and will not go to a professional. Mainly because now it is quiet enough, and also because it wouldn't change the vibrations and coarse nature of the sound.
• So what will you do next reegarding the noise?
  • Enjoy this car for as long as possible and accept the nature of the noise
  • Consider a gasoline car, and/or luxury  car which is more insulated for the next one

 And that's it. Now onto the next thing...

[mbgar]

You placed a layer of 10mm foam ontop of the alubutyl layer on the hood, is there a difference between alubutyl only and plus the 10mm foam?

 

you could put patches of alubutyl onto the metal where your spare tire is, that would deaden as well. (not engine but like the foam you put there)

[chimaera]

The only way to reduce engine vibration is to change the engine mounts. If the car is 14 years old and still on the original mounts, they are almost certainly shot to pieces and replacing them will make a big difference.

 

In general, to eliminate noise you want to do two things. First is stop large (metal especially) panels from vibrating because this creates a lot of noise. This is what the rubber sheets do, and even relatively small amounts of material can make a big difference.

 

Second is reduce 'echoes' in empty spaces between panels i.e. stop any noise generated by vibrating panels moving through open spaces within the bodywork. This is what the foam is for. If you have room, the best stuff is the foam with the little pyramids on it, and make sure they face the empty space.

[mbgar]

I guess changing the engine mounts can only be done by taking out the engine and cannot be done by normal people with a normal amount of tools and no lift?

 

Edited 23 March by mbgar

[chimaera]

8 hours ago, mbgar said:

I guess changing the engine mounts can only be done by taking out the engine and cannot be done by normal people with a normal amount of tools and no lift?

 

No, it is done without removing the engine. You do the mounts one at a time and make sure the engine is supported when you are removing the mount.

[xtp77]

20 hours ago, chimaera said:

The only way to reduce engine vibration is to change the engine mounts. If the car is 14 years old and still on the original mounts, they are almost certainly shot to pieces and replacing them will make a big difference.

 

 

Interesting idea. The car is 11y.o. (I get mixed up with the other car). 

 

Any idea of the cost of doing that at a mechanic? Even a ballpark number 100 EUR? 500? 1000? 

[mbgar]

12 hours ago, chimaera said:

No, it is done without removing the engine. You do the mounts one at a time and make sure the engine is supported when you are removing the mount.

 

Could you do a tutorial on how to replace the mounts, what parts are needed and what tools?

[chimaera]

9 hours ago, xtp77 said:

 

Interesting idea. The car is 11y.o. (I get mixed up with the other car). 

 

Any idea of the cost of doing that at a mechanic? Even a ballpark number 100 EUR? 500? 1000? 

My mechanic just charged me €363 in labour to do the job, plus the cost of the parts. It's about 4 hours work to do the whole lot.

 

8 hours ago, mbgar said:

 

Could you do a tutorial on how to replace the mounts, what parts are needed and what tools?

 

I had a mechanic do it for me because I didn't have the time or energy to tackle it myself. The procedure is in the service manual which you can purchase from Skoda at https://erwin.skoda-auto.cz/erwin/showHome.do

[xtp77]

On 24/03/2024 at 09:38, mbgar said:

 

Could you do a tutorial on how to replace the mounts, what parts are needed and what tools?

 

Definitely beyond my capabilities, but here is what I found.

 

 

 

 

On 24/03/2024 at 18:02, chimaera said:

My mechanic just charged me €363 in labour to do the job, plus the cost of the parts. It's about 4 hours work to do the whole lot.

 

Thank you for providing the cost of changing the engine mounts. I may have to go down that route. As the vibration has some mechanical origin.

 

About the vibration: The car vibrates in the 1200-1400rpm range, particularly when I push the accelerator pedal to get more power, like a climb. I was testing yesterday with the DSG, and when in 4th, 5th, 6th at that range, when I push the accelerator pedal to 60-70%, it shakes noticeably, and it is very clear on a climb (I can't press it fullly because then the DSG will down-shift automatically even in manual mode). Otherwise, it is independent of speed, and as I just changed the wheels and tyres for summer, independent of those.

 

Looking at the forum, it seems the source of the vibration may be the engine mounts, or the air intake.  Any other ideas are welcome though!