I can say from my experience that the humming is kind of sporadic, and depends on various things. Sometimes, without changing anything in the setup, it's very very faint (something that wouldn't bother me), other times is significantly louder with no explanation. I have noticed it also depends on what is connected to the Icon (eg unplugging my sub changes the loudness of hum) - but none of those things completely eliminate it. My point is it's pretty variable and there could be any number of reasons why some people experience it or not. Such is the nature of ground loop issues, I think.