Hi,

 

I recently bought this car and it starts making low tone noise at around 1100 rpm. It's hard to describe so I've included link to video where you can hear it. It's happening in regardless of gear and also in neutral, when stationary and moving, mostly when throttle is applied, but I've heard it a few times without throttle applied at speed around 50 km/h.

 

Do you know what could be wrong with it?

 

Engine: 2.0 TDI CR 110kW

Transmission: 6-Gear DSG

Model year: 2016

 

Link to video: https://www.youtube.com/watch?v=DPM4KIdDazs

 

Thank for all responses.

Is the A/C turned on? It may be the A/C compressor, they often get noisy when running low on refrigerant gas. Turning A/C off would confirm.

Edited 23 May, 20206 yr by xman

It's happening with both A/C on and off.

Something to note. It is a constant pitch, as engine RPM changes, so less likely to be anything connected to a belt (water pump, pulley, beatings etc).  Although failing bearings can come on like a switch at their resonant frequency. But this doesn't sound like that.

 

Although would have been nice to hear it at higher RPM.

 

Is it a stuck stepper motor? How does the car drive.  Error codes?

 

If you open the bonnet can you locate the sound?

 

I know the Turbo has a separate electric coolant pump. It could be that kicking in as the RPMs increase?

Edited 24 May, 20206 yr by digifish

Car is running very smothly, everything seems to work fine. I've ran diagnostics on it and there's nothing serious.

 

I've made a recording in higher rpms. Here it is: 

 

The noise cannot be heard outside, only inside.

Cool, thanks, the noise definitely does not change pitch with engine RPM, I isolated it here for you...

 

 

The frequency is almost exactly 300 Hz. The straight line below....

 

 

The pitch is almost exactly 300 Hz

Edited 25 May, 20206 yr by digifish

Thoughts...

 

Cooling fan bearing ?

 

Electric turbo coolant pump bearing ?

 

Stepper motor noise (dithering) - Electric intake flapper valve? 

Edited 25 May, 20206 yr by digifish

Interesting, in your second video at 11 seconds when you increase revs quickly the sound momentarily stops...which may indicate bearing noise. Resonant. In which case could indeed be a Water Pump bearing. 

Tommorow I will go to mechanic with the issue. I'll post here when I'll know more

@digifish That is above and beyond diagnosis for a forum! What a hero you are!

10 hours ago, boydeee said:

@digifish That is above and beyond diagnosis for a forum! What a hero you are!

 

Actually I have an interest (work) in the audio field.

 

Training an AI with enough recordings like this, when correct diagnoses are made, would be able to identify most issues.

 

https://arxiv.org/pdf/1901.08247.pdf

 

 

 

Edited 26 May, 20206 yr by digifish

11 hours ago, digifish said:

 

Actually I have an interest (work) in the audio field.

 

Training an AI with enough recordings like this, when correct diagnoses are made, would be able to identify most issues.

 

https://arxiv.org/pdf/1901.08247.pdf

 

 

 

That's really interesting! My work uses accelerometers to listen to bearings, gears, driveshafts, pumps and airframe vibration for health monitoring so I can appreciate what you do.

Really nice work you both guys do! Today I was at mechanic, he also thinks it's some sort sort of electric pump, but unfortunately he didn't have much time today to further investigate the issue. In about two weeks he should have time to look deeper into it and then I'll update you with the info.

So I know what's causing it. A kind user on different forum found out that the noise is produced by Exhaust Pressure Converter (part number 1K0 906 627 B). It is fasten right to the other side of dashboard. I don't know yet if it caused by the converter itself, or by bad grommet. I've ordered new converter and will let you know.

Thanks for the update. So Item [17]? So this is a vacuum or pressure leak?

 

Could be a hole in a diaphragm or o'ring leak indeed.

Edited 11 June, 20205 yr by digifish

I've replaced the pressure converter but the sound still remains. So it must be some part of it's holder that's transferring the sound into the cabin. I've also ordered new grommet, but I don't have it yet.

 A few days ago, my dealer called me about some service action called 23CE or CA2823CE. It is about some fuel lines i think. May be  is the same? Someone  else ?

2 things that might be of interest:

 

I have a 220 petrol Superb and my engine makes a similar noise at similar revs, always has done, I thought it just sounded like the air intake or something changing pressure...?

 

My fuel lines buzz like hell at about 2000rpm sometimes, it’s because of vibration - they aren’t clipped in place they just run inside a metal channel under the car. I used some strong metallic tape to fix them in place but the sound has recently returned - gonna try some expanding foam or something

So today I've changed rubber grommets (part number 20 in the diagram a few posts above) and the noise disappeared

The part number is 046 131 887 if anyone would be interested.

On 20/06/2020 at 01:33, pr0digi said:

The part number is 046 131 887 if anyone would be interested.

 

Thanks for the update, so it was a vibration isolation failure? I assume the grommet is for NVH?

Edited 22 June, 20205 yr by digifish

No it wasn't. It was old rubber rings that were passing vibrations further into the cabin trough body. They're part of the bracket that holds the valve.

Edited 23 June, 20205 yr by pr0digi

@digifish Ignore my last post, I must have misread your post. You are right about vibration isolation failure.

1 hour ago, pr0digi said:

@digifish Ignore my last post, I must have misread your post. You are right about vibration isolation failure.

 

I had been meaning to come back and ask