Very loud bang inside the cabin

[CajoLajo]

This morning when I was driving to work at 60km/h I heard a very loud bang. It originated from the inside of the car close to passenger side door of the cabin. It is hard to tell. It was so loud that my ears were ringing for 2-3 minutes after. The best I could describe it is a gunshot noise/explosion. The radio was on, very quiet. Early morning drive with very little traffic. I have been unable to find anything wrong with the car. I inspected the coil springs, they seem to be intact. Has anybody experienced this? Could it have something to do with radio or seat belt pretensioners (I assume they are fitted). The car drives just fine.

[Breezy_Pete]

Have a play with the seatbelt on that side, and/or where it plugs into. I think your idea about pretensioner misbehaviour might be right.  That said, I'm not sure how it would behave after such an event, compared to normal.

 

[iriches]

If a seat belt pretensioner has fired then the buckle will be noticeably lower, as it will have been pulled towards the floor of the vehicle.  It should also have lit the airbag warning light, IIRC.

 

A broken coil spring would be a far less unusual failure, and these can be difficult to spot unless the car is up on ramps.  You may experience some clunking over bumps or when turning the steering lock-to-lock if a spring has broken.  

 

Edit: thinking about this more, a seat-belt pretensioner firing would require lots of things to have gone wrong.  I assume from you description there was no passenger in the seat?  If there was, they would most certainly have noticed the tug on the belt if it had gone off.  if there was no-one in the seat, then then it's even more weird that it managed to fire.  IIRC, it shouldn't go off if the seat is empty / no belt is plugged in.

Edited 1 December, 2020 by iriches

[AllanDJ]

A broken spring is far more likely, I had that on several occasions when I had a Ford Mondeo Estate years ago. Both front springs broke within warranty period but Ford refused to even consider any goodwill payment for them, even though there were clear signs of bubbles in the metal where it broke. When a spring breaks you will certainly know about it but afterwards it is possible to drive the car for a while fairly normally depending on how the broken parts are touching.

[varaderoguy]

I had a problem with my first Scout (a 2009) - I came back to it at the car park and literally opened the driver door.  There was an almightly BANG from the front passenger side.  I looked high and low, but there was no visual damage.  So - I suspect a front nearside coil has failed.  You will need a new spring and a struct top (because the struct top will have been damaged).  Cost me three years ago about £200 to have it all fixed (turns out the Scout's suspension springs are more expensive than standard).

[Breezy_Pete]

1 hour ago, iriches said:

If a seat belt pretensioner has fired then the buckle will be noticeably lower

Do you mean the bit the belt plugs into, in the middle of the car? My reading of the ETKA parts list is that the pretensioner lives in the reel part, not the 'socket': https://skoda.7zap.com/en/cz/octavia/oct/2015-753/8/857-857060/

 

Whilst I agree that a broken spring is far more likely, I've experienced one or two of these and I wouldn't describe the experience as ear-ringing loud. Nor as sounding like it's in the cabin.

Thorough, jacked-up inspection of all springs would be logical if there's no obvious change in the seat belt behaviour though, taking to a tyre place and getting it fully lifted might be quicker and easier. 

Edited 1 December, 2020 by Wino

[CajoLajo]

I cannot see any broken springs. Not an expert. I just remembered, the other day I was getting the shopping out of the boot when I heard a loud bang. Short but very loud. Gunshot type. I did not pay attention because I thought the garage door was flexing due to 40 c + temperature. It was not obviously. What kind of a sound you would hear when a spring goes bust?

[J.R.]

52 minutes ago, Wino said:

Do you mean the bit the belt plugs into, in the middle of the car? My reading of the ETKA parts list is that the pretensioner lives in the reel part, not the 'socket': https://skoda.7zap.com/en/cz/octavia/oct/2015-753/8/857-857060/

 

 

You are correct, I had to replace the seatbelt reels in the Yeti after an airbag deployment, they are exchanged against ones where the pyrotechnic charge has (hopefully) been replaced.

 

If it has deployed then the seatbelt reel will be inoperative, it would take a very specific combination of faulty wiring for it to deploy on its own, not impossible but as the wiring does not pass through the door bellows then its unlikely.

[Breezy_Pete]

Thanks for confirmation @J.R.

Looking at wiring diagrams, there seems to be two variants, one with just  the actuator local to the seatbelt reel, one with a control module also local to each.  The latter sounds - if anything - more prone to failure.

[varaderoguy]

1 hour ago, CajoLajo said:

I cannot see any broken springs. Not an expert. I just remembered, the other day I was getting the shopping out of the boot when I heard a loud bang. Short but very loud. Gunshot type. I did not pay attention because I thought the garage door was flexing due to 40 c + temperature. It was not obviously. What kind of a sound you would hear when a spring goes bust?

No - you won't see the break - because it probably would have fractured at the top of the spring (where it goes into the top of the struct).  Yes, the sound you experienced sounds exactly like this.  It caused by corrosion and metal fatigue.

Trying to find the noise on Youtube is hard work, but this sounds familar - basically a metallic bang.  Its caused by the force of the tension of the spring releasing.

 

Edited 1 December, 2020 by varaderoguy

[CajoLajo]

20 hours ago, varaderoguy said:

No - you won't see the break - because it probably would have fractured at the top of the spring (where it goes into the top of the struct).  Yes, the sound you experienced sounds exactly like this.  It caused by corrosion and metal fatigue.

Trying to find the noise on Youtube is hard work, but this sounds familar - basically a metallic bang.  Its caused by the force of the tension of the spring releasing.

 

No corrosion. Springs look like new at 40,000km. The car drives fine so far, no noises that I can hear when going over speed humps . I will take it to my mechanic to inspect. The explosion I heard did happen so it must have originated from somewhere. 

[Breezy_Pete]

Have you tried pulling that passenger front seatbelt out?

[Ootohere]

@CajoLajo

Have you looked in the boot at the spare tyre / wheel if you have one, or at the repair kit if you have one?

[CajoLajo]

18 hours ago, e-Roottoot said:

@CajoLajo

Have you looked in the boot at the spare tyre / wheel if you have one, or at the repair kit if you have one?

Spare tyre is intact.

18 hours ago, Wino said:

Have you tried pulling that passenger front seatbelt out?

All seatbelts work.

The car goes for inspection on Saturday, I tried today but all hoists were occupied. The mechanic said, I would know if it was the spring. Not really reassuring but I really don't hear any noises. This rear coil spring related VW recall is interesting https://static.nhtsa.gov/odi/rcl/2019/RCRIT-19V188-9241.pdf

My car has the same springs as Golf Alltrack so there is a  chance that the spring was faulty if it really exploded. I checked if the part is available in Australia and sadly it is 4-6 weeks wait to arrive from Germany once ordered ($260 for one). Would there be a matching after market spring? I could not find one for part number 5Q0-511-115-AM

[AndyC]

Read this thread with some interest. Its been a few years now, but something similar happened to me in my Mk1 Octy. An almighty bang/thump while just driving. Never found anything wrong, nothing had broken, everything worked. No debris on the road.  It was mooted that it might have been some sort of feedback through the sound system causing the 'bang'. Never happened again and noone came up with a better idea.

 

Andy

[nidza]

I had a stone in the tire, causing vibration I couldn't determine where it was coming from. Stopped twice to check the car, nothing visible. Ended with a loud bang, as you are describing, on the highway, no harm done, with vibration immediately gone.

[encephalopathy]

2 hours ago, AndyC said:

Read this thread with some interest. Its been a few years now, but something similar happened to me in my Mk1 Octy. An almighty bang/thump while just driving. Never found anything wrong, nothing had broken, everything worked. No debris on the road.  It was mooted that it might have been some sort of feedback through the sound system causing the 'bang'. Never happened again and noone came up with a better idea.

 

Andy

same here - had this happen a couple of times on my mk2 octavia - was through the speakers/sound system. completely random.

[CajoLajo]

All four springs have been inspected and found to be in very good condition.

[BBDom]

I had the same on my 2018 SE Hatch, driving on the dual carriageway at a steady pace and it sounded like someone had shot the car. I put it down to a glitch with the car infotainment system - I can't find anything else it could be.

[manamp27]

On 01/12/2020 at 20:25, CajoLajo said:

This morning when I was driving to work at 60km/h I heard a very loud bang. It originated from the inside of the car close to passenger side door of the cabin. It is hard to tell. It was so loud that my ears were ringing for 2-3 minutes after. The best I could describe it is a gunshot noise/explosion. The radio was on, very quiet. Early morning drive with very little traffic. I have been unable to find anything wrong with the car. I inspected the coil springs, they seem to be intact. Has anybody experienced this? Could it have something to do with radio or seat belt pretensioners (I assume they are fitted). The car drives just fine.

Hi - did you manage to find the cause of the bang?

[CajoLajo]

5 hours ago, manamp27 said:

Hi - did you manage to find the cause of the bang?

No, it remains a mystery .

[superbdreams]

I agree with the coil spring as being most likely, it could be a tiny piece right at teh top.

However

Just to throw it out there- a LI-on battery will explode with a sound like a gunshot if overcharged , is there a portable  vehicle starting device in the glove box?