So let me preface this first by saying that what I'm about to describe is probably unrelated to your issue based on your description. Unreal Engine games since at least UE3, have had a weird sort of memory leak that doesn't always pop up. I really don't know what causes it. It affects games I've played by both indies and big publishers. Many games avoid it entirely; nobody I've ever been able to talk to has been able to lick it. Doesn't seem to affect all computers either, so I'm guessing there's a broad hardware/OS combo that's facilitating the problem. The upshot, and why I'm even mentioning all this, is that it causes sort of what you're describing. As the memory leak gets worse, the game starts to stutter, slow down, the audio gets chunky, and after a while it gets to a point where you need to close the game and restart it(or failing that, it'll crash on its own eventually). I have never found a workaround or blanket setting that can stop it in affected games. Again, I don't know if that's what's happening to you, I'm just about to install the game myself. I never ran into it playing the E3 demos though.