Noise from back of S4

Driving my 2001 S4 today I heard what sounded like a motorcycle following me at a distance. The sound turned out to be from my car. It isn't an exhaust noise because it is related to speed
rather than engine power. At 30-40 MPH it is like the rumble of a motorcycle. At 80 it is higher pitched, a low pitched whine. (I didn't think to check what it sounded like at 120.)
It's from behind and to the right of the driver's seat. It sounds about the same with the sunroof open or closed.
Any idea what this might be?
The car has 66,000 miles on it. The rear differential seals were replaced at 48,000 miles, when the dealer did a detailed inspection for the last free service.
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John Carr ( snipped-for-privacy@mit.edu)

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Possibly a wheel bearing.
Tony 96 S6

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The right, rear wheel bearing on my 2001 S4 was failing (the quoted guess below was correct). I just had it replaced. Is it worth preemptively replacing the other rear bearing? I'm going to be driving a long distance this summer and if it's going to fail I'd rather replace it now rather than in the middle of a road trip.
The mechanic said this is a common problem on Audis.

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John Carr ( snipped-for-privacy@mit.edu)

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Wasn't really a guess. I've heard of the B series chassis having more than its fair share of bearing failures. I have a 96 S6 with 109000kms and rear bears are just fine - inspected 6 months ago. Had a front replaced but the front wheel had taken a whack or big pothole.
Tony 96 S6

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I've lost a couple front tires to potholes but it was a rear bearing that went. You wrote that your bearings were inspected. Is that possible on an 01 S4? The bearings are supposed to be maintenance free, meaning they work until they break then they have to be replaced.
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John Carr ( snipped-for-privacy@mit.edu)

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wrote:

than
rear
the
Yeah the bearings are sealed units, they basiclly go on untill you can no longer bear the noise, there is no test to check they are gone, and my car passed 2 MOT's with noisy bearings, there was no play or noise at low speed.
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On 28 Mar 2005 01:08:37 GMT, snipped-for-privacy@mit.edu (John F. Carr) wrote:

Is it safe to presume your S4 is left hand drive? If so, by my estimation, "behind and to the right" would put it somewhere as near as the Torsen center diff (tho probably not "behind" enough), the rear drive shaft and associated u-joints, to perhaps as far as the rear diff and inboard CV joints on the half shafts.
Otoh, wheel bearing failure can transmit some pretty harsh noise through the drive train. Could a rear wheel bearing be within the scope of "behind and to the right?"
Either way, if you still have a bit of warranty left, I'd scoot it into the shop. If it's as obvious as it sounds, they ought to get it squared away...
/daytripper '00 s4 6spd
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Rear right wheel bearing. Experienced the same last year. JP Roberts

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