I suddenly got a humming sound towards the r. rear of the car. It changes with car speed, not RPM. I had the bearing on that side replaced about a year and a half ago. What are the most likely causes? (1997 A4 1.8t Quatro)

 

I just replaced mine. When you drive does the sound change when going around a curve such as an on/off ramp? Depending on if you are going left or right it may get louder or quiter, putting more of less force on the bearing. If you are able jack up the car and spin the tire to see how it sounds. Grab the tire and try to wiggle it back and fourth. I had a little play in mine, there should be none.

 

That would be the first thing to look, was it a first line part used
or second line ? most second line stuff doesnt last that loong
The noise would change going round corners, like the left would make noise
when you turning left and vice verser ...when the load goes on that side.

Secondly it might be your rear end, Check fluid and fluid quality

 

First rotate your tire to the front. c
If it follows the tire, then it is tire noise, not a wheel bearing.


If it stays in the back, check the bearing or rear differentila oil.

 

Do these differentials lose oil or go bad often? Where do you check it?

 

No they aren't weak spots, but yes they can leak, and yes they can wear especially if the car was abused, towed incorrectly, or had mismatched tires for a prolonged period of time.

 

im having the same problem in mine 1998 a4 quatro. its at its loudest around 50-60 mph and the only thing i can do to make it go away is accelerate but once i begin to slow down it gets really loud. im fearing it my dif.

 

I had a loud humming noise while driving, andit was my hub bearing. Sealed hub bearings about $65 each. The faster i went the louder it got. Annoying.

 

G'na replace my front bearings this weekend. My passenger side has that distinct humming. Although it is not necessary, I'm replacing both as it would only be a matter of time before the other one goes.

I had teh car on a hoist and spun each tire manually. The one with the defective bearing had a sound when spun while the others were relatively quiet.

Good luck!

B