[Gooch4130]

2008 BMW 335xi
120k miles
Logic 7 System replaced by AVIC-8100NEX and 2 4 channel pioneer amps

Work done consisted of replacing the fuel injectors and plugs. No whine before this work, bad whine after....

Just got my car back from a reputable indy shop and noticed a bad alternator whine in the rear deck speakers (no other speakers exhibit the whine). I do have an aftermarket head unit (Pioneer AVIC-8100NEX) and 2, 4-channel pioneer amps. This setup ran fine for the past 2 years and suddenly I am getting whine in just the rear deck speakers after the aforementioned recent service. I noticed it the instant I got in the car. Oddly I have had to reset the clock a few times as well, but that no longer appears to be an issue. Worth pointing out as it only ever happened after this service.

Mechanic stated he did not touch anything on the car aside from disconnecting the negative on the battery during the work (battery is roughly 2 years old). I had him go back and triple check all grounds, etc and he was not able to find anything. Battery tested out okay. The whine increases in frequency with the RPMs. He used a multimeter to test ground and manually grounded the engine block to the chassis to rule that out.

I did as much troubleshooting as I could, after the mechanic retraced his steps and handed the car back to me. Disconnected ALL RCAs from the amps, whine is still there. Removed the fuse from the power feeding the amps to the battery and the whine is gone. Obviously no amp, no sound to speakers, so not a viable solution.

Put the fuse back in, noise is back. What I determined, after additional testing, is that the noise is ONLY present if BOTH amps are connected via molex connectors that feed back to the speakers. Connecting either amp gets rid of the noise, but only allows whichever speakers are connected to function. Reconnecting both amps via the molex connectors, causes the noise to return. At the moment I am just running the 4 front speakers off of one amp. I assume there must be enough power draw when both are connected to cause the issue to surface?? No clue...

Any suggestions would be greatly appreciated. Next step is to take my car to the person who installed the audio equipment, but I hate to sink more money into the car.

Thank you in advance for the help...this is driving me insane. Sounds like a dentist drill when the issue is occurring.