Thanks for the sugestions, 'but...'
I restarted the PC after installing drivers
, also tried changing the default theme and changing it back. Nothing :/
Also, now that I know the name of the sound I extracted it and checked it in some media players - the sound is not corrupted, I played it in slow motion and it sounded ok (except for the slomo :P).
Only when it plays in windows on at normal speed in media players it gets distorted.
Also, tried to play around in the drivers with sampling and other things - no change.
Tried other themes - most of them are ugly :P - but all sounds appear to play fine.
I would never guess that I could miss windows sound... :>