Audio Systems: Occasionally no audio, factory stereo, c2r

Question
I have an'03 Silerado fully loaded with stereo system and CD player. On occasion I get no audio from my stereo, door chime does not work when key is left in, low fuel chime does not work, etc. However, the stereo has powere and is displaying as if it is working but no audio output. Then the audio magically comes on. The next time I get in the vehicle everything may work just fine. What could cause this? Ignition switch?  

Answer
you remove the radio!!!  this is not the factory stereo that came with the vehicle

that is why you are getting all this problems
you need this

http://www.oemautosound.com/pc-218-135-pac-c2r-gm24.aspx

and don't go to the same stero shop that install your radio