I had a Creative X-Fi XtremeMusic in my rig and I constantly had distorted audio - manifesting in the form of 'crackly', echoing sounds. Really frustrating, I tried all kinds of solutions including a clean uninstall of the audio drivers, replugging the sound card in a different PCI slot, etc. For a while everything would be fine, and then back into crunchy-sound-land...
My rig used to have Windows XP Pro as the OS, and the sound card worked perfectly. It was only after I changed the OS to Vista that the woes began.
This is probably not the solution you want to hear, but after 2 years of despair I flogged the card on eBay and bought myself an Auzen X-Fi Prelude 7.1 card. Although that is still an X-Fi it works beautifully in Vista, absolutely no problem with the sound since.
-=W=-