Take the sound card out, uninstall SB drivers and sweep them then try. A nice little buzz after a freeze is exactly what I was just getting last week. I took my XFi Extreme Music and tossed it in the trash. Vuala, no more issues.
Good catch, didn't see he was using a sound card.
Had issues with my X-Fi Extreme Music as well - was essentially causing my desktop to not boot 75% of the time if it was turned off, and would occasionally cause it to BSOD. Removed it and never had any issues again.