Crackling noise D2X

[Luca1]

Hi

Am experiencing a crackling noise when I play COD4 in Vista Ultimate 64 through Asus Xonar D2x.

Finished playing F.E.A.R 1 and sound worked great all way through.

Updated drivers. Checked speakers through onboard audio and speakers work fine.

Could my card be gay? (excuse the wording, it late, i tired, been trying to figure this out)

Any help or suggestions would warrant much appreciation.

Thanks
:Luca