I have a 12/02 build 2003 e39 in which I recently installed the 13th gen bt module from bimmernav. I have a retrofitted nav system with two amps tied into the 12 & 26 pin connectors in the trunk. Prior to installing the bt ulf I hod no alternator whine / noise in the system. After plugging in the ulf I now have a faint alternator whine and I am trying to figure out how to get rid of it.

As I have the euro armrest I did not install the try and only have a hack momentary button for pairing. With the euro storage tray in the armrest there really isn't room to keep the button plugged in so that connector is open. I thought that this might be an issue but keeping the button assembly plugged in does not solve the problem.

As I noted I have a set of amps powering the stereo. These are pulling power off of a direct connection to the battery with a separate single ground to the chassis. As the ulf ties into the audio system and it is not tied into the same ground used by the amps I think that is causing the open loop. So I think if I tie the two grounds together it should solve the problem.

I would just tap into the ground wire going to the ulf in the 54 pin harness and run a line to the ground used by the amps. Or, would it be easier to run an additional ground wire from the ground block the amps are connected to to ground point in the 12 pin connector?

Any help on this would be greatly appreciated!