I had an issue where my sound would just totally cut out for a few seconds, then come back, over and over. In BF3 and Diablo 3.
Discovered it started doing this after I updated my audio drivers to the latest version from Realtek's website. Their new drivers caused the problem. Re-install didn't fix. So, I rolled them back to the audio drivers from ASUS website (my mobo), instead of Realtek's website. Fixed my issue.
Believe I rolled back from 2.68 to 2.55.
May be worth a shot to try different audio drivers.