I recently had my checked by someone for a grinding noise - intermittently be heard and they tell me: they found the differential is grinding. From their test schedule it is the pinion bearing inside the differential that is causing the noise. This bearing housing is sealed and is not available separately and as a result the differential needs to be replaced as a unit.
I also asked them to check the gear as the 2nd gear almost felt a bit metal - like metal was touching I thought it would need lubricating.
They found the clutch is very soft and taking low. The gearbox appears to be fault free, however the clutch springs have become weak and the clutch and flywheel would need to be replaced in order to rectify the symptom. The flywheel is not able to be skimmed as it is a dual mass type.
These are extremely expensive to replace and I am wondering if it is normal for a brand new BMW - I am first owner to give these problems at just below 150000 km.
The flywheel can be surfaced and the clutch is a self adjusting type that BMW knows is troublesome, the differential is another issue, individual parts are not available from BMW perhaps, but, BMW does not manufacture the bearings and they are available if ordered by number from a bearing supply house. All of this sounds like the shop you are dealing with may not be aware of what is possible