I have been trying to find out why I hear a hum from all my speakers when pressing on my brakes. If I disconnect the rear speakers RCA from my amp the hum goes away. I have now plugged in a ground loop isolator which is masking the problem but I am wondering what is causing it. I tried swapping the front and rear speaker rca from the amp and the sound comes back. Could it be the amps grounding, the rear speakers RCA, or a connection within the rear speakers themselves? Getting behind the radio to run new rca cables to test is not easy and if it could be the amps ground would rather try that first.