It seems I am getting the typical differential whine due to age on a
1992 BMW 320i.  The noise is coming from the back and is only slightly
dependent on speed.  My question to the group is, could it be something
else, bearings?

The history of the problem is that about 20,000 km ago, I started
having this rubbing sound at slow speed turns. It would show up every
now and then and the feeling was as if something was holding the rear
wheels together and not letting them turn at different speeds. It would
only happen at slow speeds (10-20 km/h).

I had a mechanic look at the differential, aparently he took it apart
and said that some limited slip surfaces were quite worn but it was OK.
After that the rubbing sound/feeling disappeared but eventually the
whining came.  Now he wants to take the differentail apart again and
adjust something to reduce the whine.

Labor cost is quite low here (in Bulgaria) and you pay EUR 100 for the
whole procedure.  However, the skill level is not always so good.  Any
recommendations what to look for?  The car has 357,000 km but drives
well and looks good.

Thanks,
Gushter