hmm. I have all components to common ground EXCEPT the head unit, but I'm only getting feedback thru 1 of the amps
Unless your house battery is a complete stand-alone bank, which it doesnt sound like it as its connected with an ACR, then at the end of the day, all grounds are common and all lead back to the engine block. In most cases, we find the root cause of unwanted noise in boats with dual banks is the head-unit is still on the factory boat harness and draws from the main cranking battery, where as the amps are drawing from the house battery.