XFi XtremeMusic card crackles and pops in Dimenision 9150 (Vista 32-bit)

I have a Sound Blaster XFi XtremeMusic card that used to work fine in my desktop. After I reformated, the card causes a crackling sound. This occurs when I move a window or scroll in a webpage/app. My system is fully updated with the latest drivers and firmware, as listed on Dell Support. I want to keep using my XFi card because it sounds much better than onboard audio, but the crackling is very annoying. I have contacted Creative support, but all I got were lists of websites to visit. I've tried swapping slots with the sound card, using earlier drivers, disabling onboard audio and unused ports in BIOS and more.

My guess is that Creative cannot write proper drivers for Vista. And get this... I tried to install an external Sound Blaster USB 5.1 XFi Surround device - the SAME crackling occured. That was surprising, since it was a USB and not a PCI device... and also why I think it's a driver issue.

Can anyone provide any help with this?? I've read it may be due to how a graphics card and sound card "fight" for PCI access... but this is mainly with Nvidia cards, and I have an ATI Radeon.

My specs:Dell Dimension 9150, Vista 32-bit (SP1), Antec 500W PSU, 2GB RAM, ATI Radeon 3870, 250GB Maxtor HDD, 400GB Samsung HDD, 1TB external eSATA Cavalry drive.

Thanks for your help!