Google "windows resource monitor". Run that in the background with the DISK tab open. When you hit a disk spike look and see what processes have disk IO. Look to see if your disk is running hard, or if it seems to be idle. A burst of disk activity can be either a lot of IO, or a small bit of IO with IO errors (bad spot on disk, etc.) causing error redrives.
common ways to start resource monitor (from www.digitalcitizen.life/how-use-resource-monitor-windows-7) "..Type resmon.exe into the Start Menu search box and press enter. Go to "All Programs -> Accessories -> System Tools -> Resource Monitor". Press Ctrl-Shift-Esc or Ctrl-Alt-Del on your keyboard, to open the Task Manager. Then go to the Performance tab and click on the Resource Monitor button..."
Running applications like chrome while you are gaming can cause this, so can the various background fix downloaders for flash, etc. You should be able to see who is doing it from resource monitor.
What kind of HDD did you install? Each maker has their own diagnostic test. Download the test and run it, you are looking for the long version of the SMART test. That will rule out disk failing. (If the disk is failing you want to copy off the data ASAP, bad disks don't get better, they fail hard.)
Aside, if disk storms are causing you grief and you find out they are normal windows stuff, a 500GB SSD is less than $150...