SB tactic 3D sigma headphones, I noticed that I get a clip/popping noise as Im listening to them.

I did what the troubleshooting said from the site: "High Proformance" set Windows XP and turned off the onboard sound card in the bios and still i get this random constant clip/popping (its not loud but enough to be distracting and annoying), it happens with all audio, movies/gaming/music. It does not happen when i use the onboard sound card and external speakers. I am using the USB THX plug for the headphones.

*UPDATE*
I just did some other tests. I tested the headphones inthe soundcard jacks without the USB THX supplied cable, no clipping/popping came out. so i thought it might be the THX sound card cable, so i loaded the program into my other computer(laptop) and tested it with the THX USB cable no clipping/popping. so i don't think the THX cable or headphones is the prob. I must be getting some conflict with the onboard sound card and the Headphone sound card what do you think?

Hardware setup
WIN XP sp3
saphire HD4830 GPU
4gb Ram
Gigabyte MA790FX-UDP5
1tb seagate 7200
AMD Phenom II X4 920

No Overclock