I have figured out the reason behind the creative x-fi crackling sounds!

[ruskoz]

I have discovered the reason why and have tested it on two different OS a WinXP home and WinXP Pro 64bit. On both occasions the combination of this sound card and running in SLI mode has caused the sound crackling. I simply disable SLI and it is gone on both OS. The reasons for this I will leave to the techs among us.

[Zantham]

This is an unfortunately well-known issue, that seems to mostly affect nVidia based boards (nForce 4 and 6xx series in particular) but has been known to happen on other non-nVidia boards as well. It is not specific to XP nor Vista, 32 or 64 bit. Some people cannot get rid of the problem, other people never experience it.