I had the same problem with hum when I added my sut. I tried 4 interconnects and only one, Autitorium 23, stopped the hum. Like you, I could move the sut around,and by touching the transformer or moving it around the hum would change.
It may or not be your problem, but like Swampwalker, your last description reminded me of how I fixed my hum problem.
It may or not be your problem, but like Swampwalker, your last description reminded me of how I fixed my hum problem.