That’s a lot of great information, thanks very much for taking the time. That’s very good to know about the mixer to mixer levels especially. I don’t really understand grounding very well, or what a groud lift adapter is or what star-grounding would mean. Before I left for work I removed a couple modules — a Doepfer BBD and a couple 2HP modules — and the noise was no longer present when I briefly tested it. But I didn’t have much time so, I’m going to test it out a bit more later tonight. ( It was a custom build, though the guy who built it just got an electrical engineering degree... )