I got this ATK 300 for a song (well, $190 but you know what i mean ) - it's freakin' awesome. HOWEVER - when I move the bass around, I get this insane loud popping from the amp. The jack is TIGHT - I'm thinking that the preamp might be bumping around in there, but I've put additional foam in there to help secure it and I still get the noise..!! Starting to make me crazy - any ideas??