Hi, our 2004 535i has an issue where on hot days, after the car is driven a little while, both the radio and CD player will have the volume drop and a huge amount of Static start. Everything in the car is stock, no aftermarket installation of anything.
That can be really hard to trace. If you’re lucky, a speaker wire or a wire to the head unit is loose and the heat makes it get a bad connection. But I suspect there’s a bad solder dot on a circuit board in the radio, in which case it would be cheaper to just replace the unit.
Hmm, where is the head unit at?