[robdrath]

Sounds like the problem I had, was a ground loop problem, since i was running to powered monitor speakers. Does the sound disappear when you plug your headphones into your mbox? If so it is like I had, since the outputs on the mbox are unbalanced, I ended up sending the outputs of the mbox into the ground lift input of a DI box, then taking an xlr from the DI box to my monitors, this cured the problem.