Originally Posted by gcunha
Just discover one more common denominator: it only happens when it's very cold. Driving me nuts. Any feedback is appreciated.
Okay, that actually makes it easier. It could be one of two things:
1. You have a bad connection somewhere in the audio system...maybe a fuse, even. Metal shrinks when cold, so a bad connection could be to blame. Does it happen once only, or multiple times? Is it related to bumps on the road, slowing/stopping/starting, etc?
2. This is pure speculation (I know almost nothing of BMW stereos after 2000), but you may have liquid-cooled tweeters. If they freeze (below -10 or so), they might stop working to avoid damage.
Or, it might be a computer problem. I know playing with the headunit is a huge pain, but could you find another to try?