Not 60 cycle hum. Just hiss, what it points out is that the return input is noisy. I love listening to the background radiation of the universe as much as the next guy but this doubles the noise floor when active. Theoretically if you just jumped the send to the recieve with a 3 inch cord you should not get much noise increase at all but in this case you do. It makes me think that there is a subtle bump in gain on the return rather than being in unity with the send. Before you ask, I did make sure that the return level was set to 0,0. Essentially this really only poses an issue with the high gain models so with the trails off, it's acceptable to me as I'm just running distortions pre the amp model. If I really need it I can use the noise gate just post the loop. It doesn't have any signifigant increase when the loop is post any amplifier model. Bottom line is if I use the Heay Distortion model instead of my stand alone pedal I have no issues. Although the real MT-2 does sound best as its tone shaping is better.