You don't have a generic (Realtek) HD Audio chipset/sound card by any chance, do you? Mine does the exact same thing you described.
I hope this isn't another damn issue with Realtek HD Audio. When I first set up this computer, I had to find a fix just to hear internet audio, so I wouldn't be surprised if the game hates this card, too.
Aw, damn it. As a matter of fact, I do. :|
I've had nothing but trouble with this card since I got it. Ugh.