I just bought a 99 A4 1.8t auto with 140k miles and I thought it was tire noise, or road noise, but now I'm pretty sure it's something else.

Maybe a wheel bearing or drive line vibration? Car has been taken care of, I have receipts for a lot of work but nothing from the drive line or suspension/wheel bearings.

It's like a LOUD hum that raises pitch and volume with RPM from 25-45 and then from 45-60 it's even louder and pulses, and 60+ it pretty much goes away, or at least gets MUCH quieter.

It sounds like when you hit a new patch of highway that has groves in it. No grinding or any red flags like that, it was quiet enough I thought it was due to the snow tires, however I'm starting to think it's more than that.

Any Audi freaks ran into something like this before???

 

when you turn to the right of left, does the sound seem to dissipate??

 

Not sure, I'll have to try that, it seems to stay the same I think.

It did on freeway turns at least!

 

its probably a wheel bearing

 

I've heard transfer cases making noise like that in transaxle setups, and an evo that had a very high pitch tone from 45 to 60 cuz of that.

 

If it changes with RPM, it isnt a wheel bearing, and if it gets better as you move faster, it isnt a wheel bearing. Sounds like transmission or driveline related to me.

 

The noise and symptoms being described sounds and acts like a bad wheel bearing that I had. Raise the car and rotate the wheels by hand to detect roughness. If it is the bearing is that bad, you'll feel it.