Audio completely stopped working, restored on restart

[rsg123]

While driving yesterday I was listening to XM radio. It randomly stopped working. Thinking it was a problem with XM, I changed it to FM radio. Still nothing. I tried making a phone call through Bluetooth, but still no audio. A few minutes later I heard a cracking noise from the speakers.
When I parked, I turned the engine off then turned ignition to Acc. The audio was working fine.
What could be going bad with the audio system?
Thanks

[szh]

Some amplifier over-heating perhaps?

Really, I am only making a swag here. You might want to run the diagnostics (how-to info is in the Service Manual - see link in my sig).

Z