massive disk activity on Vista Ultimate

from time to time my HD just starts getting really active and stays active
for a long time...

Resource monitor Disk shows System Volume
Informatio\{fe9abd70...}{3808876...} running with no reads but 25,000,000+
writes (B/Min).

Can anyone clue me into what this is? Unfortunately the HD is not as quiet
as I'd like and besides working out the HD its annoying me

Dell XPS480 E8500 3.16Ghz
Vista Ultimate SP1
3GB DDR2 800Mhz, 500GB SATA, Intel 82566DCV-2 Gigabit NIC