I've occasionally had problems like this, though I never knew exactly what they were. They always seemed to have something to do with the interface between my application and my system's sound set-up. You could check how sound is being processed by your OS and try a different method. But I think your first choice should be your audio drivers. Do some cleaning up and see if that fixes it:
Follow the instructions in this tutorial
. Make sure you remove any codec packs you may have, as well as desktop versions of divx
, (you can reinstall them later if you want) and pay particular attention to the registry cleaning part.