My 5 cents:
1.Scroll down All Apps to the "Windows Administrative Tools" , Open the "Defragment and Optimise drives". Turn OFF the process.. In its early stages, it could be very active and using your resources.
2. It could be the index service consolidating the disk base. This should ease up over use.
3. Check, if you have a third party antivirus program, that it is configured correctly and is not overdoing its function. Some can be customised to make complete scans at very frequent intervals.
4. Have a look in settings - Update and security, and see if there are any large updates being downloaded/installed.
5. Open the taskmanager - Startup, tab. See if there are any programs which are running resident, which you could possibly turn off.