Ive dont have one but Ive saw alot of guys on hear trace this problem back to Pioneer headunits. They say grounding your rca jacks solves this problem. Try doing a search on this. There was recently a thread made specifically about this topic.
yeah, if you have a pioneer head unit, grounding the RCAs helps a bunch! I also had this happen because of an amp i had and the RCA's had interference AT the amplifier itself. What equipment do you have?