I noticed strange occasional slowness in some games, and when I checked in Process Explorer, whenever my FPS drops in StarCraft or WoW, CPU usage was at 100%. Then I checked which processes were causing high CPU load, and it turned out that it was audiodg.exe (which was started by one of svchost.exe). I googled around and found this article (and some more which basically suggested the same) -- http://technicallyeasy.net/2009/03/fix-audiodgexe-high-cpu-usage/
I did what it told me to do (disable enhancements for playback devices), however problem wasn't solved by that: I still have occasional spikes of audiodg.exe's CPU usage. Does anyone know what other solutions might be for that?
I am using Windows 7, and my audio is onboard VIA HD Audio (my motherboard is M2N CM DVI and my audiodriver's version is 22.214.171.12400)