Hard Disk Activity When Computer Is Idle

CAUSE

When your computer is idle, Windows performs various housekeeping activities. One such activity is compacting the virtual memory swap file after one minute of inactivity. This is done to conserve disk space.

You can confirm that this is what is happening by running the System Monitor tool and monitoring the Swapfile Size item in the Memory Manager category. When the hard disk activity is finished, you should see the Swapfile Size file decrease.