What is this sound!

[Macadamia]

I know how difficult it is to diagnose a car sound even when you're there to witness it! But this is pretty distinctive, if anyone has heard it they will recognise it.

It's hard to isolate exactly where the sound is coming from. It's almost certainly outside underneath the car and not something INSIDE the car vibrating. To me it sounds like a heat shield vibrating or even rubbing against the drive shaft but I've been under the car multiple times to check and they're all clear, in place and well secured! Its coming anywhere from the second row seats or further back.

The sound occurs on and off, under all different road conditions, on and off road, different speeds. the most common seems to be going up an incline or in a saddle at the start of the incline. but it's also completely inconsistent. it might happen once on a SLIGHT incline I drive daily and not happen again for a month.

There's no loss of power, can change gears with paddle shift without any hesitation or problem and on the 4x4 screen the centre dif is unlocked. there are no errors. The car is under no stress.

This one that I captured is actually the longest it has ever gone for in a single go. usually it's just a blip and gone. this was on a very slight incline, at about 1200rpm.


https://youtu.be/-8VJ86kTmeU

[Tombie]

Does it sound like it’s central under the vehicle?

Check the rear shaft centre bearing carrier.

[Plane Fixer]

Check the cat heat shield under the LH side passenger floor. I had that a while ago.

[Briar]

Check the cat heat shield under the LH side passenger floor. I had that a while ago.

Ditto. That exact same thing happened to me once. I had to drive through a a storm and hit some decent puddles on the LHS of the road. The upspraying water hit the heat shield and forced it into contact with exhaust. After I worked out what it was, just bent back into place by hand.

[Eric SDV6SE]

Seems to me heat shield rubbing against exhaust, or on suspension component. Noise seems to coincide with slight rises in the road.

Check heat shields on passenger front wheel well

Another point could be around exhaust where it crosses the transmission pan - you will need to pull the belly pan off. This is a double layered plastic and aluminium pan, dirt and rocks get trapped in between and then rattle. Alu heat shield gets bent up and contacts exhaust crossover pipe.

[HarryO]

Seems to be a series of back to back sounds- To me it sounds like the knobs on the wheel tread rubbing on the wheel arch cover of something similar like that..

[Macadamia]

Does it sound like it’s central under the vehicle?

Check the rear shaft centre bearing carrier.
what am I looking for here? The boot is intact, no splits, no excessive movement and the heatshield isn't deformed and has no wear marks to indicate rubbing.
172593172594172595


Check the cat heat shield under the LH side passenger floor. I had that a while ago.
this one looks well secured also.
172596


Seems to be a series of back to back sounds- To me it sounds like the knobs on the wheel tread rubbing on the wheel arch cover of something similar like that..
I'm on standard 255/55/19 wheels so almost no chance of rubbing and all the arch panels are secure.
172597

It's got me stumped!

This is the only heatshield that isn't totally secure. I couldn't get the bolt for the compressor guard over it. I'd be surprised if it was this though. I can't even hear the compressor inside the car so doubt I'd hear this. All the same I've zip tied it secure and will see how it goes.

172598

[Eric SDV6SE]

This is the only heatshield that isn't totally secure. I couldn't get the bolt for the compressor guard over it. I'd be surprised if it was this though. I can't even hear the compressor inside the car so doubt I'd hear this. All the same I've zip tied it secure and will see how it goes.

172598[/QUOTE]

I think we have a winner there, also check the transmission sump guard in the right of that picture.

[HarryO]

Hi Mac - Did you find it ?

[LuckyLes]

Hi,
I had the fuel filler pipe vibrating against the inner guard a little while ago. took me a while to work out where the noise was coming from. Another time I had a stick get jammed between the heat shield and exhaust.
LuckyLes

[Macadamia]

I think we have a winner there, also check the transmission sump guard in the right of that picture.


Hi Mac - Did you find it ?

sadly not. I secured that one loose heatshield but it hasn't made a difference. I feel like the sound maaaay be coming from around the drive shaft CV joint - I guess to rule it out I will remove that heatshield completely for a breif period and see if it still happens. and will continue to rule out things until I find the cause.

[josh.huber]

sadly not. I secured that one loose heatshield but it hasn't made a difference. I feel like the sound maaaay be coming from around the drive shaft CV joint - I guess to rule it out I will remove that heatshield completely for a breif period and see if it still happens. and will continue to rule out things until I find the cause.

Don't have to remove it, jam rags behind it

[HarryO]

It’s hard to make out from the video but does the sound happen when the suspension is pushed up by the bumps in the road - or - does it happen on flat sections..

[Macadamia]

It’s hard to make out from the video but does the sound happen when the suspension is pushed up by the bumps in the road - or - does it happen on flat sections..

I feel like it happens mostly just coming out of a saddle or when there's a change in incline of the road so to some extent yes when the suspension is pushed up... but its definitely not hitting the bumps. it is such a gentle incline in that video. Its also intermittent - it happened once on a route I drive daily and then never again :Thump:

[DazzaTD5]

As others have mentioned...
I had a customers D4 do this yesterday.
Although all the pressed alloy foil heat shields were in place, I moved them slightly, as in with my hands to change their shape, fix it.

[Graeme]

Check the dust shields on the rear brakes for cracking at the bolt holes.

[imaz]

Do you have rear A/C? Mine vibrated like hell as the blower was imbalanced/dirty.

[Pat]

Check that the strip between the front windshield & roof has not come loose. This has vibrated at speed on occasion. I just give it a thump in the middle.

[Macadamia]

Check the dust shields on the rear brakes for cracking at the bolt holes.
I'll see if I can get to them without removing the wheels, otherwise will check on them next time I rotate.


Do you have rear A/C? Mine vibrated like hell as the blower was imbalanced/dirty.
no rear A/C. just the poverty pack for me!


Check that the strip between the front windshield & roof has not come loose. This has vibrated at speed on occasion. I just give it a thump in the middle.
It *is* loose (a pressure washing accident) along with the a frame plastic trim which both occasionally vibrate in the wind but what I've capture is definitely not them. The sound is coming from somewhere mid to rear of the underside of the car.

Unfortunately I'm back in lockdown so no long drives to test out after removing the headshield over the drive shaft.

[SimmAus]

Sounds like an interesting game this; I know you’ve said it’s from underneath, but it sounds a lot like my roof rack panel vibrating (when it’s loose)…

[Pippin]

Sounds like an interesting game this; I know you’ve said it’s from underneath, but it sounds a lot like my roof rack panel vibrating (when it’s loose)…Or a badly fitting 'A' pillar trim.

[Hoges]

I couldn't quite work out how many times the noise occurred over a set period of seconds because the "chimes" kept beeping ....however, my initial impression is that it's some sort of 'sympathetic resonance' vibration.

Can you replicate the sound by giving the engine a "blip" with the accelerator pedal while stationary in the driveway or does the vehicle have to be moving at say (guessing here) 60+ kmh?

Does it matter if the engine/exhaust is fully warmed up or not?( ...thermal expansion may be part of the explanation)

If it only occurs while driving then it's fair to assume it's driveline related...

Does the rhythm of the "brr... brr... brr..." sounds vary with the speed of the car or with engine rpm at a steady speed?

Even though panels etc of whatever size appear to be properly secured, they may still vibrate. Double check all the fastenings of the components mentioned by others in these posts.

If it's driveline related and speed dependent, I'd suggest carefully checking UJs and CV joints for undue "play" to begin with...

(Hope this helps...can be most frustrating ...if not...pls forgive my lazy Covid lockdown musings... ![bighmmm]

[Graeme]

I'll see if I can get to them without removing the wheels, otherwise will check on them next time I rotate.
Give them a tap with a large screwdriver or similar from under the back. If one rattles or vibrates then it needs to be removed and repaired anyway.

[Macadamia]

some closure finally as I didn't get anywhere with popping heat shields on and off.

The D4 went in for a service today and they called to say the prop shaft bearings had collapsed and I could either replace the bearing or the whole shaft. They recommended the whole shaft as the replacement bearings are poorer quality.

I was already planning on getting the alloy coolant distributor installed while it was in so it's turned into quite a pricey service >_<

[Tombie]

Well there you go.. centre bearing carrier [emoji41][emoji106]

[Eric SDV6SE]

They recommended the whole shaft as the replacement bearings are poorer quality >_<
OEM replacement bearings should be fine. Propshaft may need to be rebalanced, but full replacement is of course nicest and easiest.

[Tombie]

OEM replacement bearings should be fine. Propshaft may need to be rebalanced, but full replacement is of course nicest and easiest.

No workshop in the UK worth it’s salt refits bearings.
Not one has had the repair go the distance.

New shaft is the go.

[loanrangie]

No workshop in the UK worth it’s salt refits bearings.
Not one has had the repair go the distance.

New shaft is the go.This is one thing I don't understand, nearly every modern rwd vehicle has a 2 piece shaft and the bearing can be replaced, must be somewhere like hardy Spicer that can do it properly.

[PerthDisco]

This is one thing I don't understand, nearly every modern rwd vehicle has a 2 shaft and the bearing can be replaced, must be somewhere like hardy Spicer that can do it properly.

It’s a plain bearing in a rubber skirt slid on the shaft with a retaining clip or similar. I just did the exact same replacement of an almost identical part in an 80s BMW. The only difference is how the centre of the shaft separates to access it. The BMW has a spline join with a lock collar you unscrew and they slide apart. The Disco shaft join is more complex in this regard with damage possible in the separation process especially in corrosive UK environments. The BMW has balance paint marks on each half you align during reassembly.

What I did learn in the bmw process was that you are supposed ‘apparently’ to preload this bearing by sliding the carrier 5mm to front of vehicle after finding it’s static position on the reassembled shaft. That’s folklore in bmw world.

The advantage of replacing the whole assembly is it’s also highly possible that one of the uni joints are on the fritz by this stage as well and leading to the centre bearing wear. Certainly this was the case for the rear uni on the bmw which was stiff and is not serviceable or replaceable.

[loanrangie]

It’s a plain bearing in a rubber skirt slid on the shaft with a retaining clip or similar. I just did the exact same replacement of an almost identical part in an 80s BMW. The only difference is how the centre of the shaft separates to access it. The BMW has a spline join with a lock collar you unscrew and they slide apart. The Disco shaft join is more complex in this regard with damage possible in the separation process especially in corrosive UK environments. The BMW has balance paint marks on each half you align during reassembly.

What I did learn in the bmw process was that you are supposed ‘apparently’ to preload this bearing by sliding the carrier 5mm to front of vehicle after finding it’s static position on the reassembled shaft. That’s folklore in bmw world.

The advantage of replacing the whole assembly is it’s also highly possible that one of the uni joints are on the fritz by this stage as well and leading to the centre bearing wear. Certainly this was the case for the rear uni on the bmw which was stiff and is not serviceable or replaceable.

Replace the uni's at the same time, simples. There only real difficulty i see is sealing the metal cover after bearing replacement but even then it can be done.
I get ****ed off by these " you have to replace the whole item for one component " statements and most are found to be bull****.

[PerthDisco]

Replace the uni's at the same time, simples. There only real difficulty i see is sealing the metal cover after bearing replacement but even then it can be done.
I get ****ed off by these " you have to replace the whole item for one component " statements and most are found to be bull****.

I’m in agreement as long as unis are ok just change the centre bearing. Some unis are not serviceable or replaceable I’m not sure what the LRs are.

[Eric SDV6SE]

No workshop in the UK worth it’s salt refits bearings.
Not one has had the repair go the distance.

New shaft is the go.

But we're not in the UK Tombie.....I understand uni joint bearings are serviceable and thr centre bearing is a std rolling element bearing. New is good though..

[Tombie]

Almost every user on D3 UK / D4 forums that has done the rebuild has had a spectacularly shortened second life on their unit.

Experienced workshops that would rebuild, now won’t, as they just cannot get the lifespan out of them.

[Tombie]

But we're not in the UK Tombie.....I understand uni joint bearings are serviceable and thr centre bearing is a std rolling element bearing. New is good though..

Geography doesn’t really matter, volume of people having the issue does.

New genuine bearing and carrier ~ $120
New entire assembly ~ $500

By the time you buy new parts for the 2 sections you have to consider the centre joint also has significant wear and tear / distance on it.
Then there’s cost of the bearing and the time to overhaul… $200 extra for a bolt in new unit is a no brainer.

This is the centre, snap shot from a how to vid.
https://uploads.tapatalk-cdn.com/20210909/1661d1ad1118c05ed69f09dcc419aed6.jpg
https://uploads.tapatalk-cdn.com/20210909/fdd6c6a157a1537e164a52994c47b0a5.jpg

[Tombie]

Replace the uni's at the same time, simples. There only real difficulty i see is sealing the metal cover after bearing replacement but even then it can be done.
I get ****ed off by these " you have to replace the whole item for one component " statements and most are found to be bull****.

In this case fitting new bearing to centre with worn mid joint and then throwing new ends on is about the same price as a HS shaft.

[Eric SDV6SE]

All good Tombie, seen that video too, I agree going new assembly is better, point is they can be refurbished