Occasional high HDD activity for no apparent reason.

I have recently upgraded my hard drive and cloned my old Win 7 partition to that. All seems to be o.k. but occasionally my hard disk starts to work intensively for less than a minute freezing everything.
The hard drive that I have used for the migration of my OS was one that had a few large files on it. I have used easeus partition manager to shrink the partition with these files and made a new partition in front of it for the OS.
I have checked the had drive for errors and bad tracks, and it looks that there are no such problems.
A look at the event viewer shows the application experience and error reporting services starting and stopping all the time.
Any idea what could be causing it? Could it be the write caching of windows? If I check the Turn off Windows write-cache buffer flushing on the device would it get resolved? Does that have an impact on the performance of an internal (non SSD) SATA HDD? Could it be due to a partitioning issue?

Any tasks running in the background while computer is idle? Virus scans, defrag, etc? What does Task Manager show while this activity is happening?

I cannot open the task manager because the system freezes when this happens. When it's over and I open it it is too late.