So far, I've asked 2 questions as part of the troubleshooting process. The last one has not been answered. Yet, still more questions are being asked.
"Anyone figure out what to check?"
No. There is not yet enough information. The noises described could be caused by a number of things in the chain, and until all questions (and subsequent follow-up questions) are answered, there will be no suggested solution.
I'll ask again: does the audio source make such noises when playing through other devices? If you don't know/haven't tried it, that's the next thing to check. If the source is DAW files, export them and listen on another device not using the console. If the tracks play clean, that tells us that the distortion is coming from the console/computer interacting somehow.