intermittent "ticking" noise e60 2004 530
i have a very annoying intermittent ticking noise that comes through the speakers for every audio source in the car (AM/FM/CD/even the tones for the seat belt reminder and when a door is ajar). The noise sounds kind of like a CD skipping and is completely sporadic, but it's consistent in the fact that it's always there.
I've search every forum I can find and haven't found this problem anywhere else. The dealer claims that I need the software re-loaded, but also warned that could cause me other issues. I think it's hardware, not software because it is worse (louder) in the summer. Also during the winter it takes about 10 minutes a driving before it starts ticking.
Any idea what this could be? I've already replaced the head unit with a radio from a 2005 530 and it made no difference. I've also disconnected what I assume is the bass amplifier in the trunk on the driver side, but the "ticking" sound is still there.