My question should probably be in the stereo section, but I'm trying to avoid the high school responses of "dude, just rip it out and put in a 15" sub".

I am currently driving an '04 S4 and the Bose system is causing my problems. When I leave work, after a hot day, the sounds comes in and out, this is in the radio function. After a little while it will come back to normal volume levels. I've had the amplifier changed with no fix. Does anyone have any ideas?