You can't diagnose a ground loop just by shutting off the components. You have to physically disconnect each component, one at a time. As an example with my most recent ground loop, I diagnosed it/eliminated the hum by disconnecting the component video cable that was hooked up from the DVD player to the television.

Any type of audio/video player you should disconnect one by one as well.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne