I currently am running a media center/server on a Lubuntu machine. The machine specs:

Core 2 Duo Extreme
EVGA SLI 680i MotherBoard
2 GB DDR2 Ram
3 Hard Drives no raid - WD Caviar Black, Green, and Samsung Spinpoint
Galaxy GTX 220 1GB
External USB Creative XI-FI Extreme Card
550W Power Supply

This machine is hooked up through an optical cable to an ONKYO HTR340 Receiver through the XIFI card.

Whenever I play any audio regardless if it is through XBMC, the default audio player, a flash video, etc, I get a horrible static sound that randomly gets louder. Here is a video of the sound: http://www.youtube.com/watch?v=SqKQkxYRVA4

This static comes in randomly, sometimes going away for short periods, but eventually always comes back.

So far I have tried everything I could think of:

1. Reinstalling OS
2. Installing/upgrading/repairing PulseAudio/Alsa
3. Installing alternate OSes, straight Ubuntu, Lubuntu, Xubuntu, Arch, Mint, Windows 7
4. Switching audio from the external card to internal Optical, audio out through HDMI, audio out through headphones
5. Different ports on receiver (my main desktop sounds fine on the same sound system)
6. Different optical cables
7. Unplugging everything unnecessary from the motherboard (1 HD, 1 Stick of Ram, 1 Keyboard)
8. Swapping out ram
9. Swapping out the motherboard
10. Replacing the Graphics Card (was replaced due to fan being noisy, not specifically for this problem)
11. Different harddrives
12. Swapping power supply
13. Disabling onboard audio

Pretty much everything short of swapping the CPU. I haven't been able to narrow down the problem and it is getting frustrating.

Is it possible that the CPU is faulty and might cause a problem such as this, or that the PC case is shorting out the motherboard?

Any kind of suggestions will be appreciated.