im having a stuttering problem in some games

[Langlest]

for some strange reason when im playing games its as if it skips a couple of frames every so often at random times, my card makes a squealing sound during some games and i have noticed that when it skips frames the sound of the card cuts out with it some are a lot worse than others, its extremely bad in oblivion (the game ran better on my old 8800gt) and it also happens in the witcher & farcry 2 (in dx10mode).. i also notice it slightly in world of warcraft but its extremely rare in that

i have no idea what could be causing this to happen, do you think it could be my power supply?

here is my system

Vista Ultimate 64
Intel Core 2 Duo E8600
Nvidia GTX280
SB Audigy 2 ZS Audio
Corsair 4GB DDR2 XMS2 PC2-6400C5 TwinX
Asus P5Q Deluxe
Corsair HX 620W Psu
120gig Maxtor SATA
300gig Maxtor SATA

i play my games at 1680x1050 & i have all the latest drivers,windows updates & bios installed

 

[Langlest]

cod was one of the few games that i didnt get any stutter in
excuse my ignorance but what is NOD32 and how can i go about turning it off?

 

[Langlest]

ahh ok i guess that explains it but i still have no idea why oblivion was running better on my old card i dont have any antivirus installed at the moment because when i noticed the problem i did a fresh install of vista

ill give the the 181 drivers a go and see if that fixes things