OK, I have a 99 ford mustang Gt vert. Im running a Kenwood Mp3 Cd player, an MTX Thunder 6340 4 Channell an Mtx thunder 5000 d-amp with a lighting audio power capicitor. i have diamond audio components throughout. I recently developed a ground loop. I replaced the 4 channell, bought brand new top of the line RCA's, new power chords, and a distribution block to sit atop the power capacitor. i cleaned up the ground (seat belt bolt in the rear) made sure the wires were at least 18 inches apart ( i have power goin down one side, RCAs down the other. After all this i still have the annoying ground loop, the only thing i can think of is that my head unit isnt grounded correctly, but i cant seem to get at the ground behind the dash. I had the shop that did the install check it out and they couldnt find it, so im going to a different shop to see what they can do, what else beside checkin the headunit ground should i have them do. I was told that it could be my wires under the hood, my spark plugs, or my alternator too, but i dont think this is the case and im not about to spend any more money than i have to. So what am i missing? Thanks in advance guys.