Thanks Lugia, I am powering over the supplied USB cable, I bet that is the the problem! I will give that a try!
-- MontanaScotty
Yep...that's approach #1, definitely. Your computer is basically a cesspool of random RF garbage on the inside, and it looks like the USB port is OK with letting that spew on down the cable.
So, approach #2 would be to use a USB cable that has a ferrite choke (it'll look like an inline "lump"), and put that choke near the computer when you reattach the USB cable, if possible. Ferrites are used in a lot of situations to eradicate noise that might move along a cable, as they effectively trap crud in higher frequencies and/or RF garbage from getting into other devices where they can cause trouble. If you MUST use USB for power, that is...otherwise, get a beefy and QUIET wallwart. Or if you have a LOT of DC-powered stuff that uses the same voltage (like 9V for stompboxes, for example), get a LINEAR power supply and then something like this: https://mfjenterprises.com/collections/power-accessories/products/mfj-1116 to serve as a DC bus hookup for those devices. This is actually rather similar to how I power my AE modular, which uses a hefty linear Tektronix supply to provide its operating DC.
Another idea, also...get a couple hundred feet of 16ga insulated wire and set up a "star ground". In my studio, this is as easy as interconnecting the various racks with a little snip of wire; your setup might require a bit more work. But the idea here is to set up a hardwired ground network that connects up to your mixer, and then making sure that the mixer is ALSO properly grounded. Done right, this not only helps with noise, but can also kill ground-loops as long as the chassis grounds are the same as the circuit grounds. When you have the star ground set up, a diagram of it should look as if everything branches off of that single mixer ground in sort of a "star" arrangement, with only that one connection point at the end of ground lines that make their way through your setup.