Sound cuts out of stereo

I'm not sure if this belongs here or in the 12v/security system forum. If it needs to be moved, move it.

A few weeks ago someone broke into my car (again) and tried to steal my stereo.. only they didn't. When I put the face back on everything would turn on and the unit would beep but no sound would come out of the speakers. I brought it to my sound guy and he checked all the wire connections and said everything was fine. While he was with me I turned to unit on and it worked. On my way home I lost the sound again. I left the unit off overnight went back and it worked fine. Now about 3 weeks later the sound cut out on me again.

Does anyone have any clue why this is happening or what I can do to fix it?