just an idea, maybe it is your proccesor not being able to cope with proccesing everything, when i had a not quite as good setup as i do now i found that if im playing music, while browsing the net and running download programs plus all the background programs the sound would not always work very welland as you say it is in certain games aswell that makes me think that it is the proccesor not being able to cope,


also not having anough RAM could be the problem,

hope this helps