Hum from input on MPC 3000....

So I have my MPC 3000 output hooked up into my mixer and then I have 1 of the outputs of the mixer hooked up to the input of my MPC 3000.. Im getting a hum, probably a ground loop. This just started and it hasnt always made this noise.. Could something be wrong with the inputs my MPC 3000 internally? I have taken apart my MPC before so I would have no problem opening it up and fixing something. I just need to know what to fix...

yeah i agree, sounds like ground loop hum, try a ground lift. cables can get RF interference as well so try rerouting you cables well away from the power cables