This, so far, only happens when there's A LOT happening on screen and the ONLY thing that I've noticed that is "clipping" (whatever the audio version of Z Fighting is, I'd call it) is the player character call outs, like: DIE HERETIC or BURN THE UNCLEAN
It's just his voice lines that clip.
I can't find anything online about this, and have no idea what's wrong or how to fix it.
It's not my headset because this is the only game that this happens in so far and it's ONLY his voice dialogs and ONLY when a lot of things are happening.
It's like there's not enough sound channels or something, and it chooses to eat just his voice lines....
EDIT: Just did some testing, and his (your characters) voice lines have the same clipping issue even when NOTHING is going on except ONE enemy nearby and slow single shot shooting.
So it's not "audio Z fighting" as I thought, unless there's some other kind.