Stereo & Electronics - help with stero problem

my stereo is acting weird. It is the stock monsoon system. At first the radio would go in and out. What i mean is while listening to the radio the sound level keeps changing from normal to real low. Now it is doing it when i am listening to a CD. Before the CD started messing up I thought it was just the anrenna, so i checked it and its fine.
Any help would be great

I had this same thing back when my car was under warranty, the volume would change on it's own and if I touched the fader knob it would be ok for a while. The problem was in the head unit, it might have just been dust that can be fixed with electronics cleaner. Since it was still under warr. GM swapped it out with a reman. headunit. Once I got the new headunit it was ok.