Doom3 Sound Shuttering Help!

[AmienZero]

just received another copy from the shop (first one was corrupted, posted somewhere in other thread). got through installation, started to play. the gfx was great, the loading was fast........but the sound! Shutters like hell. it kills my mood of playing Doom3. i tried using the no-cd crack (maybe it'll go away if i load from the pc), but no luck. tried extracting all files (maybe it shutters while loading the game) still no luck. tried reinstalling again, and again, no luck.

so i decided to try the demo doom3 instead. but! even in the demo game the sound shutters. so maybe it's my pc. updated all drivers (ATi Catalyst 5.3 and Via Audio 590b). still shutters. lowered the game quality. no luck.

can somebody help me? i'm so desperate to play this game!

my specs :
P4 2.0GHz
512MB DDR RAM
ATi Radeon 9600
AC97 built in sound (could this be the problem?)
HDD 40GB + 6GB + 160GB
Headphone Speakers (does it matter?)