Whining noise - rear end

[Mr K]

Polytek'd the rear diff mount the other day (70shore). Its made a huge improvement! However, it has also made the car make an humming / whining noise from the rear at speeds over 70. It only happens when on the throttle, as soon as you back off it stops. I need to have an have a proper play with someone in the back to listen, but I think its from the right rear, and didnt seem to be effected by turning (although it was only sweeping motorway type bends).

I suspect its always had this issue, its just that only now is it audible.

The car has always suffered from drive line take-up when slow speed maneuvering / reversing and sometimes when accelerating hard for a period then backing off - although this does seem to have almost gone. This slack remains with the polytek'd diff mount but is more of a mechanical clunk now than a dull thud.

How can I work out of its the diff / diff bearings / CV joints (and which ones) / wheel bearing (maybe the whining is un related to the drive line slack?).

Help please! the drive line slack wasnt really a problem and may be unrelated, but the whining noise will make me go mad!

Note, the car has new RS4 snub mount, lemforder gearbox mounts, and 034 motorsport road spec rear diff mounts. The drive line slack noise is deffinitely from the rear drive train.

 

[spartacus 68]

Rear bearings are notoriously difficult to pinpoint. Been there myself this year. Garage replaced it but must have damaged the bearing when installing as it was there again in less than a month. No play on the wheel, but you can identify by sitting in the back with someone else driving. Fit FAG, etc. A rear diff gear oil change is worthwhile too.

 

[Broken Byzan]

on ours i have dubbed the slack/clonk a "feature" because i can't see me replacing the lot at great expense to maybe make it slightly better

 

[spartacus 68]

Agree with Broken Byzan regards potential expense of replacing parts to make a slightly better. However rear wheel bearings (assuming that's what the noise is) are a complete pain in the butt and it won't get better, but worse. I'd replace the bearings as pairs initially, then complete a rear diff gear oil change. This could be done for under £200 or less if you remove the hubs and take them to a garage to get the bearings pressed out.

The chances of the rear CV joints going are remote. The rubber boots rarely go, compared to the fronts, (more chance of an ABS reluctor ring breaking). The clunk could be a worn central prop-shaft bearing. More details here: ok guys.. whats she worth? one reluctant sale coming soon! - Audifans.net
Audi don't sell the central bearing and will ask for £1,600 for a new quattro system + fitting + VAT.

I noticed they're being sold on Ebay. No idea of quality, but got to be worth it if there's lots of play. BRAND NEW PROPSHAFT CENTRE BEARING AUDI A4 B5 1994-2001 30X15MM 153MM 69MM | eBay

Again, not a huge amount of financial outlay if you can do the work yourself, or an Indy that won't charge you an arm or a leg.

I doubt the picture is a B5 propshaft bearing, so don't read too much into it, in terms of mounting holes, etc. You'll need to get under your car to inspect.

 

[Tom_B]

The centre diff bearing is a BMW part - Jason at all German parts will sell you one - tapatalk won't let me put up a picture of the part - when I get to a PC I'll post it up. It cost me £37 I think which is not much more for a quality bearing in my view.

 

[Bradderz_1988]

Does it sound like a wheel bearing ?? And does it between 3/4k revs on part throttle and goes as soon as you let off ??

If so then ive just replaced the rear diff which has cured that problem but brought another whine on which i think is the torque tube bearing as aragorn had this problem on craigs and has the same issue on shed iirc so im just leaving it till i win the lottery and can afford to buy all the drivetrain parts new from audi lol

Mine still has the shunt but not as bad as it was ive yet to put rs4/034 engine mounts on, i currently have 034 snub and bracket, 034 track density g/box mounts, polytek'd 85 shore diff mount, apikol rear diff bushes and as above its now a feature of the car !!

 

[Tom_B]

 

[Mr K]

Thanks for all the input chaps.

Whining noise - Engine revs dont seem to effect it, its purely road noise and starts from 10mph! It does seem to be on the driver side rear, which would point to it being a bearing. It doesnt do the 'waaa waaa waaa' thing that Ive had wheel bearings do in the past, its just a constant whine (like a failing diff would do). What I cant quite get my head around is that it only started when I polytek'd the front diff mount. Im struggling to beleive that the whining of a wheel bearing would be emphasises by a mounting so far from it. For now, im going to ignore this one and concentrate on sorting the clonk.

Clonking - I did think that the polytek'd diff mount had reduced how often the clonk was there whilst driving, but it seems as frequen as ever - only louder. The plus side, is that its now audible outside the car so I plan to get a trusty helper to listen whilst I make it clunk. It can be done at standstill just by bringing the clutch up. I SHOULD be able to work out atleast if its diff, centre prop bearing, etc and then go from there. Once Ive worked out what it is it shouldnt be too hard to fix - a second hang diff should be more than £100, and the info on the prop bearing on here is invaluable. Its just a matter of working out what it is!

I could always put an old diff mount back on to take it back a tolerable level of 'driveline slack' but all the time its a mechanical clack it cant stay like this. Id much rather fix it to be honest.

I too think its unlikly that its a CV - the rears hardly do anything. but Im running out of ideas. Will have a good listen for the clunk, and maybe do the diff oil next. If I sounds like the diff is the clunk clunk and new oil changes the whining then its a done deal that I need to swap it out.

Chaning the rear diff mounts did change the noise, but changing the front mount has had a massive effect on it.

 

[Bradderz_1988]

Mine has the same clunking when you lift the clutch up to the bite very quick im just going to ignore it till something snaps or falls off lol it doesnt really do it driving only when parked or maybe setting off harshly !!

 

[Mr K]

You recently changed the diff and mounts didn't you? Did this change it?

 

[Bradderz_1988]

No not really its always been there even with the replacement diff it still does it, did it with normal mounts and still with polytek diff mount and apikol diff hanger mounts !!

I too get the whine but i think thats down to the solid mount transmitting noise through the cabin !!

 

[Mr K]

Weird. This doesn't fill me with hope. Fingers crossed that now its loud enough to be heard properly I can now locate it. Otherwise I'll stick a standard diff mount back on it and sell it on I think. Had enough of this one almost, spent a fortune on chasing faults.

 

[Bradderz_1988]

Hey mine has loads of little noises that i would love to sort but i no id end up bankrupt if i did look in to them,

if i win the lottery then i will be setting up an account with audi and 034 as they would get a very big order of parts for the drivetrain etc and maybe some widebody panels

Back to reality ..... it sounds daft but why not dynamat (if thats what its called) the rear end these cars are too good to get rid off as one day they might be up there with some of the classic audis we all love today !!

 

[spartacus 68]

I suppose one other thing you can do is to remove the driveshafts from the rear diff (undo the splined bolts) which will allow you to rotate the wheel and listen to any rumble without the rear diff being engaged. Personally I'd replace the rear bearings. When one is worn out it resonates and the sound is almost impossible to identify when driving.

I had exactly the same thing with my car earlier this year. Got an Indy to replace it then I had to go back a further three times to get them to check it. In the end they reluctantly replaced the bearing again. The only thing I can think is they damaged it pressing it in, so it was making the same noise within a month.

Runs fine now. Get a little vibration through the gear stick, but I assume its either a snub mount or engine mount. I can live with it as I'm sure there will be other things that require attention.

Regards the clonk I take it you've checked the exhaust mounts thoroughly before you start stripping out the rear diff?

 

[Bradderz_1988]

It could well be the exhaust as it does sit close to the diff hanger i had it on a 4 post ramp to check but you couldnt pin point the noise due to the ramp noise moving back and forth.

The whibe is definately not wheel bearings as they are both new SKF units and ive replace them twice just to be sure !!

 

[Kingfisher]

OK, I have the clonk issue ( well wife's car does ! ) however.............

Car had low 80k miles and driven relatively sedately by her and briskly by me.


it also had a real whining noise for ages and I thought it was a rear bearing.

Car went into Vagtech at Milton Keynes for new front suspension and other stuff like cam cover leaks etc and I mentioned the whine.

Nothing wrong with the wheel bearings
HOWEVER
they did say that there was an odd wear pattern on the rear tyres ( MOT man had also mentioned but I ignored as they were well legal)
AND
the lower rear inner bushes were shot - allowing the lower arms / axles to effectively rock back and forth when going onto / off the power.

They Polybushed these bushes ( others were OK - I was happy to do all the rear bushes but they said not to waste money !)
they advised me to get two new rear tyres.
I did and all we get now is a very quiet driving experience. A by product was that it stopped wandering on the road - no longer being steered at the rear !!
So have you check all the bushes and particularly the lower inners?

 

[Bradderz_1988]

My lower inners are shot and going to polybush the rear and change the tyres soon so will see how i get on !!

 

[aragorn]

Problem is, transmissions and differentials ARE inherently noisey.

This is why the standard car has huge soggy rubber bushes, to absorb all the noise and harshness from the components.

I've done the same thing as you in the past, and i'm beginning to realise the error of my ways. The standard car, when new, didnt have a soggy diff mount, didnt clunk, and was smooth and quiet. Parts wear out, and these bad things appear, and everyone fixes it by upgrading the worn out mounting with rock hard uprated stiffened parts, then moans that its noisey/harsh/whatever. I notice it when i jump out of my car into my brothers E90 BMW, and everythings quiet. Theres no vibrations from the stiff engine mounts and whining from the stiff gearbox and diff mounts etc etc. In mine, the dash vibrates at idle, the stereo fascia vibrates at certain engine RPMs, the diff whine is deafening at 40-50mph etc etc.

What it needs in reality, is new standard OEM rubber parts to put it back to how it was when it left the factory.

Obviously some of these mounts are expensive, which is why alternatives are often seeked, but i think in terms of the overall driving experience, OEM is the way to go for a daily driven car.

I'm going to try replacing some of my stiffened parts with new OEM bits and see how i get on.

 

[Broken Byzan]

OK, I have the clonk issue ( well wife's car does ! ) however.............

Car had low 80k miles and driven relatively sedately by her and briskly by me.


it also had a real whining noise for ages and I thought it was a rear bearing.

Car went into Vagtech at Milton Keynes for new front suspension and other stuff like cam cover leaks etc and I mentioned the whine.

Nothing wrong with the wheel bearings
HOWEVER
they did say that there was an odd wear pattern on the rear tyres ( MOT man had also mentioned but I ignored as they were well legal)
AND
the lower rear inner bushes were shot - allowing the lower arms / axles to effectively rock back and forth when going onto / off the power.

They Polybushed these bushes ( others were OK - I was happy to do all the rear bushes but they said not to waste money !)
they advised me to get two new rear tyres.
I did and all we get now is a very quiet driving experience. A by product was that it stopped wandering on the road - no longer being steered at the rear !!
So have you check all the bushes and particularly the lower inners?

https://www.dropbox.com/sh/9jo6xok8abfzbz4/982WCuxRaR

Our avant sounds droney, wheel bearings seem ok, no grumble when turned( well one is new anyway) Around 40mph it's worse. I am going to change the diff as I cannot see the bushes doing it on ours. What exactly did it sound like?

 

[Kingfisher]

Like a wheel bearing !
No , seriously -

It started as low as 30 mph with a slight but distinct rumble from the rear, ( afai remember ) seemed to be regardless of power on, off, freewheeling, clutch in or out. ( should be worse under power - as the rear toe out would increase ??)
By about 70mph it was loud enough that speech was getting difficult - and the radio - well not worth bothering about.
Although it did this most of the time there seemed to be some times when it was more noticeable than others - so not totally consistant

I see where Aragorn is coming from- although the 4 poly bushes are only part of the rear axle bushing so may not be too critical with noise issues.
Front snub was replaced with RS4 version so still OEM but upgraded.

Is the RS4 rear diff mount the same as TQS / S4 version?
ditto the engine / gearbox mounts ( they may well be in a different place, 5 speed versus 6 speed, but possibly the actual mount is the same?)

 

[Broken Byzan]

@kingfisher, and this turned out to be inner lower rear bushes?

[video]https://www.dropbox.com/sh/9jo6xok8abfzbz4/eBdS0U1wqm/VID00002.MP4?m[/video]

 

[Kingfisher]

Must have been.
Car was having front arms etc etc replaced and some engine seals. Hence it was with them for a several days so they could work on a cold engine.
Dropping the car off I mentioned the 'whine' thinking it was a bearing and they came back to me later in the day about the worn lower inner bushes. (The owner ran a RS4 for several years - now has RS3 )

They replaced those four bushes ( two each side) and suggested I get two new tyres ( Goodyear *** 2). I did and the noise was no longer there.
That's all I can really say, it was nearly two years ago so my memory is not so clear about finer details this far down the line !
It also had a 4 wheel alignment obviously with all the new front bits.
I would have thought bushes would be easier/quicker than the diff - to start with?