The first thing coming to mind is as audiobob mentioned.
Is this a ground loop hum?
You can try using a cheater plug on the Odyssey assuming it has a ground plug on its power cord (oddly enough the Anthem amp i had last week did not).
The Halo amp did have the ground plug on the power cord but it ALSO had a feature for lifting the ground loop (a switch) on the back of the amp such that no cheater plug would be required.
When i first had the hum from the Halo, i tried out the ground switch but the sound was not quite like a ground loop hum so i figured that that was not the issue. If it is that audible with the Odyssey and it sounds like a constant 'tone' i would guess that is the problem.
Beyond that, send the unit back to Klaus or in the least, give him a call.
