blazed is right about hooking it to the fuse box. that is kinda unheard of in the radio world.
also did you mabey get a small hole in your power wire when dragging it through the car? because if it was grounding out some where that could cause all kinds of problems and would explain why it fixed it when they disconeccted it.

i always run my rcas on one side of the car and power wire on the other so i dont, by chance, get frequencey distubance in my speakers

 

cool man that is the best way to run your RCAs !!