I've also been having this problem. Changing my in-game audio mixer setting and changing it back helped the problem for just a few minutes, but since that time it's been continually getting worse. It's taking more than three full seconds for the opening-a-menu sound effect to play, or the chat-cursor sound effect, because it's chopping itself into so many tiny pieces.

I've just changed to DX9, which has helped just enough that my city background music will now play correctly, but this is a temporary measure at best, and I still haven't tested it in combat, which is where the worst distortion occurs.