Originally Posted by NZBM

Thanks Fifty150hs for the reply, that pretty much explains it. The whine is driving me nuts!!

I've been working on cars for years, but I'm very much a novice when it comes to car audio, always stick with factory units.

The repair to the BM53 unit was carried out overseas- had to mail the unit, so wanted to be 100% sure that was the issue before retuning it.

I had a good look trough the whole car today, checked all the cables front to back (there is so much wiring in the back of these X5's!), checked the earths etc.

I removed the BM53 unit, and plugged in a single DIN aftermarket head unit via an adaptor at the BM53 harness connector- the whole system worked without issue- the whole factory harness/amp/speakers etc. No high pitched whine.

Plugged the BM53 back in, high pitch whine is back. There must be an earthing issue with the repair that was done?

I've emailed the repairer about returning under warranty to get sorted properly, so we'll see how we get on.