installed parrot blue tooth in 92 850. i now notice noise which increases in frequency with increase in rpm. it may have been there before. in the old days, i would say it is alternator noise(or generator for my old cars) and we installed a condensor in line. if this is the cause what is the fix for 850"s without killing alterantors or computers?

there was a bulletin regarding radios on BMWe31FAQ.com that covered cleaning contacts on the antenna and the antenna amplifier in the c pillar.

You may also want to clean your battery terminals and check your chassis grounds at the batteries

Hope this helps

I put a sony head unit in my car had the same noise
I took the speaker ground off the chassi aginst the insatll instructions
and ran the ground through the factory harness
and the sound went away