bearing, differential?

[s4ohio]

New to the site had my 2001 s4 just hit 100,000 miles for a year now.

when i drive between 55 and 70 i can hear a loud hum coming from the rear end. I believe it is from the passenger side. I tried swerving to see if it was a bearing but i could not tell. I had a sway bar link rub on my axle on the driver side and break recently. I replaced that and still have the noise. Tires are all good and wearing evenly. I have a small leak in the rear diff, not enough to even get on the garage floor just gets the case wet. I tried changing the rear diff fluid and there was no shavings in the oil and it still wines.

car is currently getting a new radiator since it decided to break like everything else does in the shop and the repair guy didnt get to take it for a drive. He said there was no noticable play in the with the wheel so he didnt believe it was the bearing.

My question is can it still be the bearing if there is no play in the wheel and whats the chances of it being the differential itself and how much will that run me.

this car has done nothing but drain my pocket for a year straight. Id have got rid of it by now if i didnt like it so much.

thank you ahead of time for the help.

[s4ohio]

bump

[RolledMySTi]

Sounds like a bad bearing

[s4ohio]

can it still be a bearing with no movement in the wheel

[AJ88CAB]

Yes, you may not be able to feel movement even if the bearing is going bad...Do you have access to one of those IR temp sensing guns. You can get them for about $35 these days. Go for a 20 minute drive then immediately measure the hub and rotor temperature. If the pass side is more than the driver side it is probably the wheel bearing. If they are the same it might not be the bearing. Does the sound change with speed. If the sound doesn't change with speed it might not be the bearing. I don't know what a failing fuel pump sounds like on these cars but that is another possibility in the same area. Or a CV joint, but they usually don't hum. Also the drive shaft bearing, but that would be more from under the car. If your real adventursome you could put the whole car up on jack stands and run it and see if you can locate the noise. But I take no responsibility for your safety if you do:)

[s4ohio]

it does change with the speed of the car and i know its not the fuel pump bc it doesnt stay when im not moving...i just keep praying its not the differential. ill see what the guys at the shop think.

[VMRWheels]

Ah, this is a tricky issue, a friend of mine was under a similar issue.

For him, the sound got progressively worse fairly rapidly, which helped determine it was indeed the differential (unfortunately). As far as a wheel bearing going bad without any sort of play, I really haven't heard of it, but then again, when you hear about wheel bearings going bad they're usually far gone. If you notice the sound to increasingly getting worse, and there are still no tell-tale signs of a wheel bearing issue it may be better to think of the worse.

I'm hoping the best for you, an internet diagnosis is pretty hard in this case! I'd say your best bet would be to take it into a well known mechanic and see if they can diagnose the issue for you.

[98a4]

I was just about to make a thread. I have a similar situation with the loud hum from 60+ increases with speed but is pretty damn loud. Noise goes away when clutch is depressed or off accel. Off accel the hum turns into a whoom whoom whoom sound about every second. Just replaced a bad rear wheel bearing before this problem started, at the same time my mechanic flushed the rear diff fluid, but I have not checked the levels yet.... Let us know if you find what the issue is.

[TozoM8]

It could be your tires. My A8 does that 50-60mph. When I swap tires it goes away.