Whining differential on a 1992 320i (E36)

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
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It's very common to think you have a bad diff when it's one or both rear wheel bearings. This has happened to me twice. Wheel bearings are not expensive and you have little to lose by changing them on a high mileage car.
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If your differential is the source of this noise, it should be very dependant on throttle setting with the noise being very different depending on whether you are accelerating or decelerating. Wheel bearing noise can become somewhat 'whiny' by causing the springs to resonate but should not be very sensitive to throttle setting. Wheel bearing noise can be amplified in a turn because the side loads on the wheel cause large variations in the bearing loads. The wheel bearing noise in a low speed turn should be a grating or crunching sound and the brake disc may rub on its pads if the bearing movement is large enough. You can jack up a wheel and spin it to see if the wheel bearings are making any bad sounds but they often don't make noise in that situation even though they are failing. I would suggest that you wait until it becomes more obvious where the noise is coming from. The differential in my 318i failed a few years ago at 300,000 miles and it was 10,000 miles from the time I first thought I heard something until I was sure that it was the differential.

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Gushter wrote:

I've had some differential whine on my '95 325i since I've owned it, for over 30k miles. It is not getting any worse so I am not going to do anything about mine. If it got really bad it would allow me to start shopping for a replacement limited slip diff to replace the current open one.
A differential whine is unique in that it usually makes the noise only when you are rolling with minimal power being applied to the gears. If you accelerate (or decelerate) the increased pressure on the gears will stop the noise.
What has to be adjusted is the tolerance between the ring and pinion gears. This can usually be adjusted by either shims on pinion or offsetting the diff inside the housing with shims. Not sure which way they do it on the BMW rear end.
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-Fred W

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