Stereo & Electronics - problem with speakers

When listening to music in my car the speakers on the passenger side of the car cut in and out. As in they play quieter than the driver side, but they ocasional get a "blip" or somthing and they play louder for maybe a half a second then they get quieter again then the "blips" continue. Any ideas on what this may be? or how i can fix it? I do have a sub and amp installed but they were installed years ago and the "blips" just recently started happening. Also the Mute button on the steering wheel started not working properly the same time the "blips" started.
Any advice would be greatly appreciated
Thanks,
Adam

Bypass the steering wheel controls and see if it still happens, could have something to do with your mute button. Or it could be loose wires between the amp and speakers, or the amp could be going out. Sometimes that stuff can be tricky to find just start troubleshooting different areas so you can eliminate them one by one until you find it.