Windows 8.1 Hard drive constantly access but Task manager only shows low usage (< 5%)

I have been running Windows 8.1 for a year and within the last couple weeks I noticed the disk drive constantly being accessed. However, the disk light on the machine is barely coming on so I looked at the task manager and the disk is not that busy. I am trying to figure out why I can hear constant disk drive activity but Windows 8.1 does not seem to think it is busy.

Is there another way to check disk access or activity?

I have tried stopping Windows Search Service, Superfetch, and something called ExpressCache but the disk just keeps sounding like it is being accessed.

Any ideas?