We just had the dif swapped out on our '95 wagon at 142k. Last Sept. started hearing a low-speed, medium-pitch whine, accelerating and decelerating. After 4 months, it could be heard at most all speeds, but you really had to concentrate.

At some point, before we owned the car, and before it reached the 105k at which we bought it, the diff developed a long-term slow leak that no one bothered with. I didn't think much of it either, but it was dripping noticably soon after purchase. Had it looked at while changing the diff mount bushings, they said, 'did you know there was no oil in this diff? Just great. So they topped it off with fresh synthetic, but too late, the damage was done. 32k later, very noisy, out it comes.

Your hunch is probably correct, especially with that entry in the service record. If its bearings, it would be more of a rumbling hum than a whine, if that makes any sense.

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1995 MB E320 Wagon
2001 BMW 530i
2007 MINI Cooper S (!)