NIS 2010 Mystery Activity

Once a day (I think), NIS 2010 does some kind of disk-intensive maintenance that isn't identified in the list of Background Jobs in the "Norton Tasks" window.  It starts when the computer is idle, and continues running until finished even if I begin using the computer.  It lasts 5-10 minutes, using about 10% of each core on my dual-core processor.  I'm curious what it's up to.  Any ideas?