Audio and Video Stutter or Popping Sounds

Hi all

Recently noticed sound and video lags during COD6. It also happens when scrolling through Albums in iTunes while a song is playing. Audio slows down as well as video.

My system includes:
3.2 Dual Core
MSI 965 Platinum Mobo
4Gig DDR2 800Mhz
160Gig HD
Logitech Z2300 2.1 Speaker System
Vista X64
8600GTS Graphics.
350W PSU
Dlink Wireless 802.11n PCI card.
My hard drive is partitioned with 20 gig set aside for XP. I have roughly 40Gigs remaining on HD.

I've tried:
1.loading latest Realtek audio, Nvidia drivers without luck.
2. Roll back same drivers.
3. Defragging System
4. Memory Diagnostics.
5. Disconnecting Wireless PCI Card
6. Playing Audio directly through headphones and not speakers.
7. Setting BIOS to default.
8. Lowering Game resolution and graphics settings (does not help, as mentioned earlier, happens in iTunes, Media pLayer too)
9. Performing System restore.
10. Removing Vista updates.
11. Updating Dlink drivers.
12. Uninstalling Avast Anti-Virus
13. Disabling background programs to enhance performance in msconfig.
14. Moving amp away form PC
15. Giving amp it's own power plug at wall and not sharing PC's power supply.
16. Anti-Virus Scan


Is there something that I am missing or not seeing? It's driving me bonkers.
Any ideas would be most helpful.

Thanks