Pc2150 i have two ppi power class pc2150 amps that i bought on ebay..both the security stickers are intact..one amp "bumps" anytime you change tracks or start the stereo or push any buttons on the amp also when u adjust the gain it continuously moves the woofer with the turning of the knob...the other has none of these symptoms..any help would be great!!thanks!!

There are several resistors that open or change value in these amplifiers if the speaker wires are allowed to short to ground. There are generally two 10 ohm resistors near the RCA jacks. These are the most likely source of the problem. If you haven't tried it yet, swap the signal lines from one amp to the other to see of the problem follows the signal line or remains with one amp.