If you have a Creative Labs Xi-Fi card, go to:
Playback Devices...Speakers Properties...Soundblaster tab
and check the box to disable Sound Blaster enhancements.
There is a memory leak caused by the 3D enhancement and possibly other enhancements to the Xi-Fi cards which causes this problem - audiodg doesn't release back memory handles it uses with the enhancements are active, or something like that. Techies could explain it better.
If you have your Task Manager open before you do this, and open up the Resource Manager, you will see you memory usage come down very quickly as soon as you disable the enhancements, and it's all down to audiodg.exe releasing the memory back.
I had this same issue...the memory used by audiodg grows over a few hours and eventually causes much disk thrashing (presumably as other apps get dumped to the swap file to make room), and sound stops working on other aps. Not until audiodg comes back under control does the sound return to the other aps.
Creative Labs should be castrated for this, as I quite like the Crystalizer effect on iTunes playback, but can't trust using it without the machine crawling to a halt.
