BMW Repair: Low pitch noise/humming from back, rear axle shaft, differential unit

Question
Hi Tino,
My car is making this LOW pitch noise from the back. When you speed up, noise gets louder but when I reach above 90kms noise seems subsiding. I was told its the differential unit because the car is a rear wheel drive. Is it right? If that's the case, is there a way to lessen the noise or do I have to replace the diff?
Another thing is since there's a noise coming from the back, you can hear the noise from middle to right. I was told to have the right CV joint bearing checked. Is bearing replaceable?
Appreciate any help/tip you can share.
Cheers
Edgar  

Answer
Hi Edgar,
I can give you general answers to your questions but it would have been easier for me to help you (which is to your own benefit) if you told me the year and type of beemer that you have.
I doubt that the noise can be lessened by anything other than repairs. Gone are the days when diffs were adjusted by mechanics(assuming that it is the diff that is the problem).
But I doubt that it is, since you say that the noise is evident from the middle to the right. Follow the advice to have the right rear axle shaft checked. Most probably it is the CV joint or the wheel bearing. But keep an open mind. It can be loose bolts holding the flange of the axle shaft or something similar to it.
First, raise the car on a lift or platform, then run the
car and put it on drive (with all the safety measures that are needed), then localize the source of the noise.
Have fun.
Tino