I've seen my Mark2 do a similar thing: Fine when plugged into some home systems, hum when plugged into others.
It's a standard ground loop, as described
here. Home stero/home theater systems can get ground loops, too.
My own home theater system does quite well with the empeg plugged into it, but once I brought it over to someone's house and got the ground loop when I plugged into their system.
Mess with all the different connections in the whole system (not just the connections between the empeg and the tuner) and see if you can narrow it down. One thing to try is plugging the player into a different AC wall jack in an attempt to get it on a different circuit.