t3 ragtop wrote:
they make noise suppressors that fit into the power wiring for the stereo. look for one of those.
I would still double check all your grounds and not just the one you have running to the head unit. All but the cheapest head units are pretty good at eliminating alternator whine so it's possible that there is a grounding issue somewhere else that's inducing the noise. RCA's can pick up noise (though it's unlikely that since you say the whine is there with or without the amp) from electronics in the car too so make sure you keep them away from power/ECU's/etc. If you have to run an RCA by a power wire cross it at a 90 degree angle. Suppressors will likely stop the whining but it also mask a possible