If you've got a sound card plugged in, disable the onboard sound in the BIOs and uninstall the driver for it.
If you want to use the onboard sound, take the soundcard out and uninstall it's driver.
Sound conflicts are one of the biggest headaches in Windows.
Also, when you were in the control panal, did you click the advanced tab and see if it was better with or without boost enabled?
One last thing to try, go into DxDiag and turn sound acceleration down to 75%.