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Vibration/resonating/boomy noise at certain RPM

Vibration/resonating/boomy noise at certain RPM

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AnneTeak

Original Poster:

46 posts

33 months

Friday 9th June
quotequote all
Hoping you can help. At around 2100rpm the car produces a resonating, dull vibration kind of noise (coming from passenger footwell it sounds). It happens in all gears and also in neutral at around 2100rpm. The noise is more noticeable in lower gears - 1/2/3.

If you hold the car at these revs (i.e. cruise control) the noise remains, when deaccelerating back down to this RPM range, the noise also comes back. No matter the length of the drive the noise doesn't seem to dispear, although does marginally decrease in volume.

The only time the noise seems to disappear is when the DPF is doing/or has done it's regeneration (you can tell the DPF is regenerating due to the computer message). Following a regen the noise doesn't come back. As I understand, DPF regeneration causes the exhaust to get very hot, could therefore this cause some heat shield in the car or something else for that matter to expand and therefore stop the boomy/vibration/rattle noise?

Car is a Volvo S60 2013, 2.0 5 cylinder diesel with 100k on the clock.

Any ideas?

Edited by AnneTeak on Monday 12th June 14:08

AnneTeak

Original Poster:

46 posts

33 months

Monday 12th June
quotequote all
Hey guys, any ideas? smile

Flibbiddydibbiddydob

11,669 posts

174 months

Monday 12th June
quotequote all
I find it often helps to mention the make, model, age and mileage of the car as well as when the symptoms started along with a bit of ownership history when posting such questions.

Had you not mentioned the also 'in neutral' aspect I would have suspected a UJ on the prop shaft.

AnneTeak

Original Poster:

46 posts

33 months

Monday 12th June
quotequote all
Thanks for the reply. Just updated the thread with the car details.

The noise remains in neutral at the same RPM.

AnneTeak

Original Poster:

46 posts

33 months

Tuesday 20th June
quotequote all
Hey guys, any ideas?
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Chromed

71 posts

57 months

Tuesday 4th July
quotequote all
Can you get it on a ramp to have a poke about? . Does it do it when stationary?. Could be a heat shield. Pully? Belt? Engine mount? Exhaust mount/clamp ?

Edited by Chromed on Tuesday 4th July 04:41

AnneTeak

Original Poster:

46 posts

33 months

Sunday 23rd July
quotequote all
Thanks for your help. Yes does it when stationary, although not so obvious to hear.

Here's a video of the noise when cold, going up and down on revs around 2100

The only time it goes completely is when the DPF is regenerating. What changes during a regen? I did think turbo related but even during regen the turbo is pulling fine.

It's also much quieter when warm although never completely goes. Also if you stay at 2100rpm the noise doesn't go with time if you maintain revs.

Edited by AnneTeak on Monday 24th July 00:25

cptsideways

12,390 posts

176 months

Monday 24th July
quotequote all
Is your car standard? eg induction & exhuast I bet its not


Google holmhurtz resonator

Mr2Mike

17,948 posts

179 months

Monday 24th July
quotequote all
cptsideways said:
Is your car standard? eg induction & exhuast I bet its not


Google holmhurtz resonator
He'd probably be better off googling "Helmholtz".

It sounds more like a mechanical resonance with a high 'Q' factor, i.e. resonance occurs over a very narrow RPM range. Something like a loose heatshield or something broken within a silencer would be common causes, but a cheap aftermarket exhaust could suffer from this (e.g. due to thin walled silencers and pipes).

When the DPF regenerates things get extremely hot in that area, so a loose part might expand sufficiently to prevent this.

AnneTeak

Original Poster:

46 posts

33 months

Monday 24th July
quotequote all
Thanks for your help guys. Car has no modifications but will check to see if the exhaust was replaced. Have it booked in to check too.

When you mention the silencer, the noise comes from the glove box/dashboard area. Would you expect the noise from there? Assuming it has silencers perhaps front and back? Definitely comes from the front of the car.

I did initially think it was turbo related, but you can hear it spool ok, even at just above idle there's a faint whir which I assume is normal.

E-bmw

2,975 posts

76 months

Monday 24th July
quotequote all
If you know where it comes from & it does it when it is stationary, I can't understand why not just jack it up, put it on stands, get someone to rev it & get underneath instead of trying to get total strangers who can't hear it try to diagnose it for weeks on end.

S0 What

3,303 posts

96 months

Monday 24th July
quotequote all
So many things it could be? if you can not find anything immediatly loose or "wobbly" underneath i'd start cheap and fit new exhaust hanger rubbers, then have a close look at the engine and gearbox mounts, they dont have to be loose or sloppy to transmit vibrations in fact the opposite, the rubber will harden with heat cycles and age where as an oil leak will make them soft and sloppy, a hard bush is a bush that will transmit more vibrations (steady at the back! ) so i could be as simple as that or more complicated like the baffles in an exhaust box loose ?

imagineifyeswill

835 posts

90 months

Wednesday 26th July
quotequote all
This may not be relevent to a Volvo but VW and Skoda have similar problem at exactly that rev range and is caused by the flexi section of the front exhaust pipe, the cure is to put a jubilee clip round the middle of the flexi, youmay need to put two and move th around a bitto cure it.

AnneTeak

Original Poster:

46 posts

33 months

Tuesday 1st August
quotequote all
Thanks for the replies guys. I have taken it to another garage although they couldn't find the cause!

Here's a video of the sound whilst the car is maintaining the same RPM (2100).

With the engine/gearbox mounts idea, would this correlate to the fact it only does it within a 100rpm range? I'll try checking the flexi exhaust part out.