If you do not see anything that is taking the time, we will have to go another route. Does this activity continue all the time or are there periods when it is worse?
One trouble shooting technique is to open msconfig.exe and go to the services tab. Check Hide all Microsoft services then disable the rest. Reboot and see if anything changes.
An alternative might be to use Msconfig and open to the General tab. Click on Selective startup and check either Load system services or Load startup items. If the problem goes away, that means it is being caused by the one you left unchecked.
What anti-virus programs have you run so far?