UT3 framerate hitches every few seconds!!!

Hey guys,
I have this annoying problem. Playing UT3, the game runs real well, high framerates 60 +, yet evry few seconds theres a slight hitch in fps. this can get real annoying especiall during fast shootouts.

I recently updated to 175.19 drivers, but i don't think thats the problem, 'cos after installing the drivers i played UT3 and never noticed any hitch ( and believe me this is easily noticeable).
I recently installed and uninstalled a lot of software, did some registry cleaning with the couple of Registry apps.
Even though i can't really point my finger at any particular event, it must be after the above cleanups.

No such hitches with Crysis though.

My system consists of

core 2 E6750
4 gb ddr 2 800
Asus P5KE
Asus 8800 ultra
160 GB Hitcahi SATA II HDD
USB Audio via Altec Lansing FX5051
Vista Ultimate 32 w SP1


Any help would be greatly appreciated.

Thanks in advance,
Scurv.