You could also try grounding the outer connecter on the end of your RCA's. Its not a permanent fix but a helpful diagnostic tool. If the noise goes away its almost always a ground loop issue. I had an Alpine EX-10 that had ground loop issues when they were first released and the only way to eliminate it was grounding the outer shields of the RCA's. Fortunately the problem has been fixed internally now and thats not an issue anymore.