Help! i have Choppy gameplay on my Radeon

I have the same problem whith every single game i play. games like quake3,halflife cs
and unreal, tend to have choppy gameplay
when theres more than 1 sound effects going on the game… Ever experienced lagg on any
multiplayer games??? well its like that but
the games pauses and reapets sound effects for a couple of seconds and then my computer
recovers after that. and it gets extremely anoying when that happens frequently. ive tried changing my sound card, my motherboard, adding 250megs of ram, and
even my graphics card to a radeon and it still does the same thing. i usually have
over 60 fps in 1280by1024 resolution when
i disable the sound on any game. but im not sure if its even my sound card thats causing the problem.