Having the same issue myself, honestly thought i was loosing my mind when it started happening till i saw this post. I've tried everything you have tried as well and even went a step further thinking it might have been my PC. So i Overclocked both my CPU and GPU as that should have resolved the issue but it is still happening any time I join a party with a friend. Sound tears, game slowing down at random times. But never one had an issue with this until about a week ago as the game was running flawless till then. Never once hit a lag spike or ever had audio issues till then. I ruled out audio driver issues as i can run discord without a problem and just to check re-installed all of my drives/updated them all across the board. I can even play all my other games like Battlefield 2042 without any issues at all. So it is an R6 issue that is causing all this and it was what ever patch they pushed out last week that is causing it all.
I'm testing and looking for a solution to the problem, but i think its going to end up being a patch the devs will have to release to fix whatever they did to cause this to suddenly pop up in the game.