My Cyber Champ amp makes a loud popping noise whenever I shut it off. Just started a few weeks ago. I've tried spraying the on/off switch with a blow-off contact cleaner without removing the sealed chassis cover but that didn't help. The cover is seemingly attached with a single screw but frankly it's sealed so tightly on all 4 sides that I doubt that the single screw is the only thing keeping it on? Any suggestions from the experts here?