you sure that your RCA's aren't getting pinched somewhere?

what kind of head unit do you have?

there have been a few cases where the RCA's we used were bad or directional.

i'd say take out the RCA's and run them on the outside of the car to ensure no interference. then gain access to the back of your head unit and mess around with the RCA output plugs to see if the noise changes when you play with it. if so, its your deck. :thumbup: