check the rca cables. also make sure your cables are not run with the power source. I would also switch the outputs on the deck to see if the rca output is bad. If you only hear engine noise in one of the amps it may be due to the fact that a sub does not operate in the range of engine noise. the noise still be present but you may not be able to hear it. I would also check the ground resistance between the head unit and amps if its higher than .3 ohms you have a bad ground point.