BY doing that you have broken the loop. It seems that you have found your way of recording audio. But, seriously, this is a right mess, this USB interference thing. I used to be able to make the most noise free recordings in my studio!
B.t.w. if you had changed to midi that might have broken the loop as well as long as there is no GND connected in the midi cable (otherwise that would introduce a loop, and midi loops are no big deal, but the USB noise the midi cable picks up is).