Add me to the list of people having this same problem.
My laptop is a VAIO FW-290 originally with Vista, now with Windows 7 Pro 64-bit.
I thought it started happening when I installed an optional update for Windows Media Center, but reading though the thread, it seems like this is not the problem... Besides, I don't know how to uninstall a windows update without doing a system restore to
a month ago.
I already have tried disabling sound effects, SRS WOW to no avail. Though the sound is a little less annoying without those features. The sound crackles/flickers/pops (whatever you want to call it) with WMP, Windows Media Center, Quicken, IE8, Firefox,
and inside XP Mode (this is more like skipping) in any combination of media players and browser.
I read in another thread that they successfully solved a similar sound issue by rolling back their driver: http://social.answers.microsoft.com/Forums/en-US/w7music/thread/d58979f8-8b01-4328-931a-2de65a57349d
Doubt that my driver was updated before this problem started happening (maybe I just didn't notice, because the sound crack/flicker is really subtle), but I guess giving this a try wouldn't hurt.
Good to know I'm not the only one having this annoying problem!