After installing windows 7, i have bad sound

hello, i installed windows 7 onto my desktop i bought a few days back. it had windows xp on it, and everything worked great. after i put windows 7 on, everything worked perfect except the sound, it makes it sound like im on a telephone with very bad signal or something. its really scratchy and you cant make out what is being said.
it is the same with speakers and headphones, no matter what it is the sound simply sucks.
i have installed drivers, uninstalled and reinstalled, everything. i just cant figure this out!
if anyone would have any idea what i need to do to get sound back onto my computer it would be great, i really want to keep windows 7 as i cant stand xp, though.

sorry if this is the wrong area, i couldnt find anything on sound being messed up.