I have a '03 A4 with a radio problem. Sometimes the sound goes away. I still have power and the problem is happens in either the radio play or CD. Any suggestions?

 

I experienced a similar problem on my 97, A4. initially, there were distortions at higher volumes then cut off from rear speaker. A check revealed a worn out speaker. The speech-coil was also found damaged. my advise is you to change the speakers and observe.
enjoy your A4,
Vwalikha.;