OEM Navigation Install

Hi everyone,
I have a 2006 HiHy and I just installed the E7006 model Toyota OEM Navigation system. Funny thing. It powers up great, the FM and AM works, CD works, except I get this loud humming noise coming from the speakers. Also I have no control of the volume. However, even when I press PWR off, the audio system stops, but the humming persists? Any ideas what this could be? It was strictly plug and play, no other connections other than REV and SPD wire. Even with those two wires disconnected, the noise persists. PLEASE HELP!