My only experience wiith ground loops was after adding a subwoofer with a 3 prong power cord. I have never owned a subwoofer that has a chasis ground screw on the back of the amp so I am not sure if that would subsitute for a 2 prong power or not. Hopefully a 600 owner chimes in with their experience.

Here is the troubleshooing guide for the EP600 in the meantime.

http://www.axiomaudio.com/troubleshooting_ep600.html

Good luck,

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne