Seems like a problem that everyone runs into sooner or later. And now is my turn.
I just installed a JH404 4ch amp to new Infinity speakers. I also have a Clarion Mono Amp running my 2x Shock Z4 subs.
Problem is that I'm recieving some noise, mostly only for a bit after turning on my power through my rear speakers it seems.
Here's the weird part now. I only have a 2x RCA out Head Unit. So I dedicated the rear out to the mono amp, and used a splitter on the front out for both the rear and front inputs on the 4ch. So why am I only getting feedback on the rears?
Maybe that your power is run to close to the rca's going back to the amp. Does the noise increase when you step on the gas, or maybe when your turn signal is on? If so try to move the signal and power wires further apart, or get some insulation of some kind between them. Hope that helps.