Thanks for continuing to follow up on this. I may have solved it, finally.
"I did everything" means -everything- that was in the list of things to do from Avid, as well as trying various other suggestions made here. Nothing I tried really made any difference except telling windows to not draw stuff inside windows I was dragging around, and even that did not solve the issue of having other apps open on top of PT, or indeed, even it drawing its own Edit window when I was actively recording.
But, all that is moot as I may have actually discovered the cause of the problem. It is indeed video card related. The Radeon 5700 XT has a known issue where it tends to make audio noise (and sometimes audible noise from the card itself) when it runs in a PCIe 4.0 slot. Which is odd, since it is a PCIe 4.0 card. But setting the slot to 3.0 in the BIOS (instead of auto) causes the noise to go away completely. I am typing this reply while listening to audio from PT
and it is pleasantly static-free.
Anecdotally, there may be a work-around driver-wise by rolling back to a version from last year. I -think- leaving it set to 3.0 should be fine, though.