When I bought my 3.0 E53 three months ago, the BM53 unit was faulty, only getting sound through one speaker, then it would cut out after about a minuet. After reading through numerous posts, sounds like a common problem. It had no speaker whine though.

I recently sent the BM53 unit out for repair, just received it back and re-fitted it, I'm now getting sound (music) through all speakers working like it should, but it seems to have developed another issue now-

High pitched whine which increases with the engine RPM's, happens with the head unit switched on or off (board monitor). If I disconnect the BM53 unit in the back, no more whine?

Not sure where to look first? Maybe something's not 100% with the BM53 repair, it only started since I refitted it after the repair.

Has anyone else experienced anything like this?

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2003 E53 3.0
2001 E46 330ci Msport
2001 E46 325i Touring wagon