I have a new XPS 420 with the X-Fi soundcard and Vista.  Often (nearly every day) my speakers will get a low pulsating sound, then a crackle, then the sound cuts out completely.  Media player won't play and Windows sounds wont occur (e.g., email notifications). Usually, after 5-10 minutes, there will be a sharp crackle and then sound is back.  I have updated all my drivers (did that right away).  Any ideas why this could be happening?  There is no common activity that is correllated, and it is unpredictable when it will occur.  It usually just happens once per day (and I don't reboot daily).  Also, when the sound is out, the headphone jack is out as well, so it does not appear to be a speaker issue.  Finally, when it happened today I immediately tried to play a song on Media Player and it wouldn't register the song as playing ( the progress bar didn't change) until the second crackle.