You probably have some DC on your main power feed. A power conditioner might clean this up for you.
Also try running a signal through the amp and see if the problem goes away. The toroidal transformers Outlaw uses saturate pretty easily when not loaded but come out of saturation pretty quickly when you start driving the amps.
Aperion Verus Grand Towers & Bookshelves, Verus Forte Center, Infinity Surrounds, Ultra-X12
Oppo BDP-103, XBOX360, Xbox One
Samsung 51" Plasma
RR2150 w/Klipsch SCR-2