Had this same problem, try grounding the RCAs, if that doesnt work replace them, and if that doesnt fix it is the radio. Pioneers are bad about the internal ground going out and causing noise. even my deh-980bt has this problem. I spent probably 2 weeks trying to figure our where the noise was coming from and its the radio. Did a install in a guys truck yesterday that had a DEH 6800 and it had aweful noise, replaced it with a Kenwood and the problem was solved.