Can anyone tell me what is wrong with my car stereo?

Recently I have been having problems with my Alpine car stereo. When i turn the car ignition on to start the car music comes on no problem however after anything from 5-60 seconds the sound cuts out but the power and display are still on, in fact when playing a CD it still appears that the CD is playing but there is no sound. If i turn off the ignition and restart then the same happens again. Every now and again the sound stays as used to and I can enjoy listening to music. I may well have to take car into car audio place but I wanted to know what i was dealing with as I assume it is only a minor problem? Any help will be much appreciated. thanks