I posted about switching to an external USB soundcard earlier. I thought it solved my popping/crackling sound problem, but no, it didn't... It worked for a while, it was much better than with the integrated sound card, but I still had these extreme (19000+ microsecond) latency spikes that could last for minutes. I also tried disabling almost everything (sound card, graphics card, usb, etc) in the device manager while looking at the DPC latency checker, and nothing...
Few months later it started to become really annoying, as the popping/crackling didn't stop. Basically, I turned the PC on, and within 3-4 minutes the crackling started and didn't stop until I shut the PC down.
Then I looked around on forums again, and I read that others had the same problem with similar Gigabyte motherboards (I have a Gigabyte GA-X58A-UD5). Somebody suggested that it might be a conflict between the Gigabyte Marvel SATA drivers and the optical drive (DVD-rom). Basically, you shouldn't plug your DVD-rom into any of the Marvel (blue) SATA slots.
So I plugged it into a non-Marvel slot, and suddenly no spikes. WTF!!! I'm constanly running the DPC latency checker now, and when I look at it after hours of gaming, it usually tells me that there was a spike, but I didn't notice it at all. So it's weird, but seems to be working. Hope it helps.