[allthrtl]

You want to also make sure that you have a good engine to chassis ground, as well as cab to chassis ground. Yes, you have isolated it to the amp somehow. Like mentioned earlier, make sure the pwr wire isn't running along side the RCA's and double, tripple and quadruple check ALL grounds. It's just electricity not rocket science.... Use an ohm meter to check the resistance between the amp chassis and ground (depending on the amp), should be .5 or less (.1 is best) Then check engine to frame and then body to engine and frame. If nothing else, make a long jumper and go straight to the battery (negative post)...If problem still persists, it's the amp or a crosstalk situation with your wiring.......I'll bet money you find it to be a problem with the ground.....

Good Hunting....