YOu can also try enabling or disabling Spread Spectrum. This is often a hidden BIOS setting, to enable hidden BIOS settings on the MAIN page of the BIOS press control + F1 and the screen will flash. Then any hidden settings or sections will be shown, look around for spread spectrum settings, there may be a few types!
Also, be sure you are using the latest BIOS, and that you are also using the latest drivers for your sound card.