High pitch sound possible ground loop issue?

[BPMSport]

I have it too on my car, but it's pretty faint. With the radio on it goes away, and I don't always notice it with the radio off. But definitely have heard it a few times.

I have an 08 6MT, every option from the factory but DCT - so ipod, hd radio, enhanced premium sound, idrive, satellite, and bluetooth/SOS.

The last software update I had was in 09. When I hooked the car up to an autologic, it said there was an AMP update available but you have to program that through MOST-BUS, not through the OBD-II port. I didn't have the fiber optic stuff with me so I programmed everything else that didn't require the fiber optic interface.

I hope we can get to the bottom of this!

[SCtud]

Ok - I actually hear it in both videos now (used headphones listening to it the second time around). This noise is different than mine and is probably even more annoying since the sound seems to be oscillating whereas mine was a constant pitch. I don't know if it's the same issue - I'd definitely ask them to fix it.

[backslashv]

Interestingly, I have the same hissing (+faint beeping) issue on my G80 M3. The dealership said they can't hear it. Not sure what to do at this point.

[jerezE90]

Reviving an old thread here but I was able to successfully DIY the solution described by SCtud and wanted to write it up for anyone else looking. Note, do any of this at your own risk as messing with high amperage wiring can be dangerous.

I recently bought a 2008 e90 M3 6MT and quickly noticed a constant high pitch sound coming from the speakers any time the car was “awake”, engine running or not, music playing or not, radio muted, ignition on/off, etc. If sitting inside the car with it off for long enough, eventually everything would power down fully and the noise would stop. My car is fully optioned with idrive, nav, enhanced premium sound ("individual audio" outside the US market). The sound is like a dog whistle, some others could not hear it but it was ruining the whole experience for me. If I unplugged either the audio-out plug on the amplifier or the MOST bus input connector, the noise would stop.

The issue is indeed the old-style 2008 era amplifier and the fix is to retrofit the newer style amplifier. The wiring is slightly different but easy to adapt.

Here is the original 2008 amp with 2 connectors, small one for the MOST bus input and big one for audio-out to speakers AND positive/negative power wires for the amplifier. Note the two large wires on the left side of the plug.




The newer amplifier has three plugs: same MOST bus input, same audio out plug WITHOUT positive/negative power wires, and a separate power plug. I bought an "individual audio" amplifier out of a 2011 E70 X5M from eBay with the harness cut and plugs still attached to the amp. Note the missing two pins in the large connector on the left side, this is where power is applied in the 2008 harness.



The newer amp will accept power from the 2008 harness, meaning the third plug is not needed and can be left empty. The only fancy wiring needed to make the new amp work is that pins 1 & 2 (the top two pins to the right of the fiber optic cables) in the MOST plug must be jumped together. The best way to do this is to add pins to the stock connector and connect the wires together. The connector comes apart, allowing you to easily remove or add pins to that part of the plug. The FCP listing for the OEM pin is called BMW Socket Terminal Mqs - Genuine BMW 61131383776, or you can get generic MQS pins elsewhere online.

My car was pre-wired for a trunk CD changer that just happened to have the wires and pins I needed, which I cut out and used. I don't recommend this but I have no plans of adding a CD changer and can easily reverse this. The plug was hidden in a fabric cover next to the amplifier location. I took that part of the MOST plug from the CD wiring, crimped pin #1 & #2 wires together, and inserted into my amplifier plug. DON'T CUT THE FIBER OPTICS!


At this point you can plug in the MOST connector with the jumper and the large audio/power connector and your stereo should work as normal. The only thing you can screw up is the MOST pin jumper, so if it doesn't work check that part first. However, the new amp in my case was still coded to run a E70 speaker system and had to be recoded for an E90 chassis.

I used the following video to get all the software and USB-OBD cable I needed to recode the amp. Again, proceed at your own risk regarding DIY coding of your car.

Once you have NCS Expert and the OBD cable working, pull the configuration from the "MAMP" ECU. Using NCS-Dummy, you should see that it is configured for whatever donor car the amp came from, mine was a E70. Change this to your proper chassis, reload the configuration to your car, and everything should be complete.

The mounting was different between the E90 bracket and the E70 amp so I had to make a couple custom brackets to attach the new amp. If you get an amp from a E90, this may not be an issue.