Update 3:20 pm 9/9/20: I've narrowed the culprit of the ground loop down to the ATEM Mini Pro. Still trying to find out how to kill it.
I searched and found similar questions, but not the same:
I have a Studiolive 32 and run both FOH and livestream audio simultaneously. I've been using USB audio out. The sound is far superior to XLR through the camera (which is what I was doing until a month ago), but the audio goes out of sync with video. So I'm trying to find the balance between over-working myself re-syncing and having better audio quality.
The issue I've run into is that now my XLR out (matrix mix out) has a loud high pitch hum. It sounds like a grounding issue, but I've never had issues with it before and I haven't moved the board. I've tried stereo and mono mix. I don't hear it on my headphone monitors or through digital routing. I've tried switching XLR ports and it still occurs. Same cord, camera, soundboard, and port as I was using before without the hum.
I've tried turning the volume up at the board and down at the camera and vice-versa. I've also tried to rout the audio directly through the switcher (BlackMagic ATEM Mini Pro).
TLDR: How do I remove a hum from XLR out?
Thanks in advance!