ACCanaris

I'm trying to diagnose a static distortion problem with my stock Bose system (2001 S4). Most of the time the sound is largely distorted but if I let it keep playing for an extended period SOMETIMES it kind of clears up to sounding almost normal. This is why I've ruled out speakers being blown all. A blown out speaker never sounds okay sometimes, of course.

My first though was a bad amp. I took it out and rebuilt (most) of the circuit board myself with soldering iron. No change in the sound. I bought a used amp from the yunk yard- also exactly the same result. No better, no worse. this made me think it might be the head unit or tuner module. I can't find any information on a tuner module for a B5 S4 so maybe it's integrated? I've heard that the antenna tuner can also cause static if the screws become loose.

I dont want to send the whole system and all its components in to be rebuilt because that would be super expensive. But I also dont want to just start throwing parts at it myself. Has anyone come across this problem?