Noise coming from rare differntial of my bmw 7 series while driving in slow speed and goes off when driving on 130 140
I would do a differential fluid flush. If that doesn't fix the problem you may have to replace it or live with the noise.
This is a common problem but there can be many causes:
1. A problem with the air conditioning belt
2. Problem with the auxiliary heater or the alternator
3. There might also be a problem with the oil seperator valve or similar gaskets or seals.
Have you tried a scanner?