problem with stereo system
 

Hey guys, i have this problem with my stereo system. There is this sound like a radio (not tuned) on the backgroun of whatever i listen, either its cd,tape, radio, doesn't matter even if i switch off the stereo system at all.And the funny thing is that it's sometimes there and sometimes it's gone.i have got dsp system, if its a usefull information. soo, if u guys could suggest what i can do with this problem. i even went to BMW service here in Geneva, and when i arrived there it stoped(bad luck):tsk: , i tryed explain the guy the problem, he sort of understood but. When i took my car the next day he told me that they could't find anything, and that the car is in an exelent shape. But when i drove away, the next day same story, the sound sometimes its there sometimes not, sometimes loud sometimes very quiet, but still it pisses me of now. sooo what should i do?:confused: