UPDATE;
Since I got home I put the car in the garage, popped the front hood and hooked up the diagnostics hoping to find something, but nothing. It was 9:45 and time to walk the dogs so they can take a dump. When I stepped outside it was cool. I walked around into the garage and turned the key on. The radio was thumpin', I had the volume set on 32.
So if this happens to you, my guess is that it's the power amp and the heat under the hood raised to the point that a thermal breaker in the unit opened. This breaker is in place to protect the amp from damage due to an overload. The unit and surrounding metal was heat soaked and took time to cool and the breaker to reset.
I wonder, if I would have turned on the A/C if the cooling air in the ducts would have found it's way to the amp? That's all from me, cheers
