OK.. I have a pioneer headunit, and a phoenix gold 1600 Watt amp with 2 12'' rockford fosgate HE2 subwoofers. Hooked up the system, worked fine, wanted to change some settings on amplifier...so disconnected..changed..he reconnected...now there is a constant thumping sound coming from the right subwoofer. However, if i connect the left RCA out into the right subwoofer RCA line, its fine, but then the left one makes the thumping. All combinations tried, in the end, if both subs are connected, one will constantly thump, or both will. They will play the music, but also make the thumping sound. However, the thumping seems to die out when the headunit plays at high volume, but at low volumes the thumping is quite loud. What is the PROBLEM!?!?! Ive ground the black wire coming out of the wiring harness to the chassis of the car, and ive grounded the black wire coming out of the headunit to the chassis of the car as well... I KNOW the amp isnt a problem, because I started the car, and hooked up a laptop's RCA out to the amp and both subs were working perfectly. I dont know what the problem is?? Im not runnign my RCA cables anywhere close to the power wire for my subs. I have a 1999 Acura 3.2 TL.