Hi Composer
You can use the Resource Monitor to check what is using the drive most when it does that.
2 ways to access it - Ctrl Panel, Admin Tools, Performance Monitor, and then click "Open Resource Monitor", or Ctrl Pnl - Performance Info tools, click Advanced Tools on the left, then Resource Monitor.
Click on the top of the Read, or Write columns to change the order to the most used or least used first and see what's using the disk more.
Then let us know what your top users are and we may be able to help.