I have a Pioneer DEH-P7500MP Head and radio reception was fine. I just installed a U.S. Acoustics subwoofer amp and now I get some radio stations, but the reception is not as good as it used to be. Some stations don't really come in at all. I used a turn-on lead, and rca cables. The amp is in the trunk mounted on the back of the rear seats. Can the turn on or rca cables be causing interference?