Hello all!
I almost pulled all my hair out trying to figure this out, and although the old forums seemed to have a lot of suggestions on the issue, they didn't help my specific situation.
PROBLEM:
I have a UX8 on a rack, and although the ins were super clean, when I would run a signal from the Reaper to one of the outs (3-8) on the back, I would get this cyclic, digital noise. It was pretty loud too, way too loud to just gate off. I tried the power stip thing. I tried switching USB ports and output jacks. I switched cables. I switched from balanced to unbalanced. Nothing.
SOLUTION:
I just started putting this rack together, and I decided to go with the fancy rubber washer screws and plastic isolation washers to keep the gear from scratching on the rack bars and since they claimed to prevent "ground loops." Well, apparently the UX8 needs to be grounded by the chassis, and those rubber and plastic pieces were preventing it. Rather than remove them, I just ran a small wire from 2 of the ground screws on the chassis to another screw on the rack bar. Noise was gone instantly. Honestly, that fix is just laziness. If I rearrange the gear on the rack, I'll probably take off the washers from the interface.
I'm posting this since it was brutal to figure out, and I never saw this as a solution in forums, so hopefully it helps someone else. I'm assuming there's other rack gear that would have the same issue too. Also, if the frame wire is a bad idea, let me know!
Cheers!