If it is any consolation, I had a similar inconsistent hum situation in my own comparisons last year of the Outlaw 755, Rotel RMB-1095 and Anthem MCA-50 amps. With exact cable swaps (using all unbalanced RCA connections), the Outlaw and Anthem were completely quiet, but the Rotel had a noticeable hum. The Rotel dealer suggested trying a cheater adapter to disconnect the ground -- not as a permanent solution. This made most but not quite all of the hum go away.