Bearing noise?

[Simon Wallwork]

Can anyone help diagnose a noise that my cars' making?

Sounds like a bearing chattering. Comes and goes but the car is quiet nearly all the time.

First time it did it was the worst. Twice as loud and vibrating. I thought it was the blower fan in the cabin. We'll all have heard the noise a knackered blower fan makes- usually goes away if you slow the fan down or turn it off.

As my daughter got out the car she slammed the door, causing the noise to restart. As I was parked, I got out and lifted the bonnet. The landing panel at the front was being vibrated. I lubed the electric fan with WD-40 as best I could and I've never heard the noise as bad since.


I've noticed it sometimes does it on startup, so it can't be the electric fan. Never as noisy as that first time though. Water pump or viscous coupling, maybe?


This morning it did it again, but quieter and it came on just as I was parking, went off when I turned the a/c off. Came back on when a/c reselected on, but then would not repeat the noise.

It's not an engine speed related noise. It makes the noise, or it doesn't. The noise does not change with rpm or road speed.

Any ideas?

[Oli18]

Not sure if this is the issue but this might help you Simon...

http://www.audipages.com/Tech_Articl...anreplace.html

-Oli

[Simon Wallwork]

Thanks Oli

I wonder if it is the fan, or something else.

At least I now know how to change the fan!

I'm worried it might be the water pump or even a cambelt tensioner. eek!

[Simon Wallwork]

Well

I've found that I can get the noise to stop if I scoosh the poly-V belt at the front with WD-40.

So it's plainly not a dodgy Water pump or a cam belt issue.

Must be an accessory driven by the poly-V (or serpentine belt).

Right now, it's stopped. after liberal spray applications of WD and 'spray grease'.

I'm beginning to think maybe the alternator. Isn't the S8 alt. a special 'low friction' thingy?

[Conan_the_Librarian]

If you start from cold and switch the air con to Eco, does it go away?

[Simon Wallwork]

Conan

It's away at the moment due WD.

It sounds a lot like a manual car does when the clutch release bearing is shot. Only quieter.

I've tried turning a/c off but it has no effect on the noise.

You only hear it at low speeds as the road noise drowns it out.

So imagine you're trickling along at 30. Noise comes on as soon as you add a whiff of power, goes away if you lift off.

[Conan_the_Librarian]

It does sound like a poly belt issue. Could be one of the guide wheels or belt tensioner. The Power Steering Pump and AC compressor bearings can go. Not heard of an alternator bearing failing, the diode pack are usually the first to go. If WD 40 cures it, unless its onerous i would keep up that treatment until the culprit shows itself. If anything on the poly belt fails it won't cause any collateral damage unless you have weedy arm muscles and can't steer to get home!

[Simon Wallwork]

Thanks Conan

Yup. can't be too serious if WD-40 stops it. I was worried it might be the WP as it wasn't changed when the timing belt was done.

I take it the poly v tension is done automatically?

[Conan_the_Librarian]

Indeed it is.

[A8 3.7]

Hi I have a 97 3.7 which had a similar noise, if it comes back open the bonnet and listen to find out which side of the engine it's coming from if it's the passenger side as mine was it can be the air con compressor clutch/pulley. If it's the drivers side it can be the alternator some were fitted with an overrun pulley which when it starts to go makes a chattering noise sometimes you can find out if it is this by looking at the alt belt tensioner with the engine running so be very careful and if that is moving up and down and not steady that could be the problem you can buy the alt pulleys on their own but you need special tools to change it. Hope this helps