Same issue here - only it does it with the onboard audio, add-in card (creative X-Fi Fatal1ty , usb plug-in audio (Plantronics Gamecom 7.1) and USB Bluetooth (3 different vendors tried).
Seems that anytime audio is used it causes blips, klicks, pops and crackles in the audio-streams.
Multiple re-installs, multiple hardware changes, 14p bios is in place, 32bit and 64bit OSes tried (Windows XP 32 and 64, Windows 7 32 and 64) every driver imaginable.
Is this normal for this model? Buggy firmware? Tempted to update to a newer chipset, but really don't want to spend more money on an otherwise perfectly functioning system.