The choppy sound's a dead giveaway that it's a Windows problem. Basically, when I encounter choppy sound, I bail out of everything I'm doing and restart the system (shut down, power off, power on). That fixes the problem about two thirds of the time. The issue is that Windows usually decides to get busy when the user needs full system hardware access the most. I've found that by getting updates, for example, under control (not to mention other software which has a mind of its own - e.g. kb3035583) I can get a decent session by http://www.gamesas.com/topic/1544320-incredibly-poor-performance-unoptimised/?p=24549666. And, BTW, Fallout 4 is not a particularly high-demand game. It's far far closer to Skyrim, for example, than, say, the current Star Citizen alpha.