Hello; I have a 2004 Silverado. I bought it new in 2004. It is a WT model with the 4,8 engine. Has 4 wheel drive. I noticed today a red light blinking on the radio/CD face after I turned the engine off and opened the door. The light blinks at about rate of every two seconds. I ejected the CD from the radio to see if that made a difference, it did not.
I do not know that this indicates a problem. It is that I do not recall noticing that flashing light before. I looked in the owners manual but could not find any description so far. There is an image of the radio showing the light location.
The radio is a base unit with a CD player. The only issue I have been having is sometimes a factory CD does not want to slide in properly. The CD will stall part way in. I can eject without any problem.

 

I'm no expert on AM/FM/CD vehicle radios, but likely it's your CD portion would be my guess. They make a cleaning disk that looks like a CD. It MIGHT help you out.