I've had this happen to me before and although very tricky to diagnose the operating system seems to be the culprit in every instance. The popping and hissing noise is also extremely hard on the ears if its the same one I've had in the past. Funny thing is it's inconsistent and not always reproducible but theres a couple things you can try short of re-installing the OS. I've had a couple glitchy glitches since moving from XP to win7 64bit with my prelude but keep in mind that the prelude is a 32 bit card not a 64bit card. Therefore it is using a shim of some kind between the two. Back when 32 bit OS's came out people were having issues with their 16bit cards and the shims they made to bridge the gap were not without their problems.
- Open the sound in control panel then open speakers in the playback tab and sound blaster in the speakers properties disable enhancements. This has resolved a couple different issues for me.
- Completely remove all the drivers make sure win7 isn't blocking your install (it blocked a few non whql drivers/software) and caused this problem.