I bet that is it, I had the same thing happen with my Pioneer Avic D3.
--David
I
n some headunits there is a micro fuse between the main ground and the rca ground, you might have blown it, happened to me on my Pioneer HU.
the fix is this:
http://audioforum.termpro.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=18;t=002066;p=0
give it a try my friend, it might solve your problem. always disconnect RCA's befor you disconnect amp/HU grounds!!
good luck,
David