Within the last week, I've noticed a faint pitch squeal from my sound card.  That is, when my volume in Windows is at 100%, it's fairly noticeable.  It's coming from the sound card and inreases in volume as system volume is increased.  I thought it was my headphoes at first but its audible through my speakers as well.  I tried different audio cables and the same result.  Normally my sound is at 75% anyways so I can barely even notice it at that level, but its clearly there at 100%.  This morning I booted my machine and the high pitch squeal was deafeningly loud.  I had to mute the sound in windows, at 100% it would make your dog howl.  So I rebooted and it seemed to fix the issue, but its still audible at the 100% level as I stated before.
I've googled it a bit and sound some mentions of a death squeal, but I'm not experiencing lock-ups like others have.  Anyone else ever heard of this?  No new system drivers or anything have been changed.  It appeared out of the blue.
Creative Sound Blaster X-Fi Fatality
Driver version: 6.0.1.1361
7-15-08