I have had my stereo installed for a while and recently, if have had problems. The stereo sometimes will turn on and start playing a CD or the radio, but there will be no sound coming out of the speakers. When i hit a bump or pothole in the road, the sound starts up, and then will play for a random amount of time, and stop, and this repeats for a while. I have checked the wiring behind the stereo and it all seems to be ok.
This happened to a friend of mine and it ended up being the stock wireing in the door. i guess there was a break in the conductor inside the insulation you couldn't see, but if you moved the wire a certain way, the sould would come back.
do you have an external amp?? could be connections on it