DiskPulse is a handy hard drive monitor that can display the changes being made to any drive or directory in real time.
Is there a lot of unexplained activity on your hard drive, for instance? Just click the Monitor button, add drive C: to the list of locations, and click Start. Right away you'll see lists of files as they're created, modified or deleted, which should give you a much better idea of what's going on.
Of course there's always a lot of hard drive accesses occurring with any busy PC, so it might be hard to pick out the more dubious activities. DiskPulse helps by also displaying a list of changes sorted by file extension, though, so at a glance you can see that, say, TMP files are responsible for the majority of hard drive activities. And double-clicking on a particular extension will allow you to view those file modifications only.
If that's not enough, then a simple Charts window will display reports to illustrate details like the "changed disk space per extension", for example.
And if you don't want to monitor your entire drive, that's not a problem: the program allows you to monitor specific folders only, and you can also instruct it to monitor specific events only. So you might opt to record only deleted files and folders, say.
The authors also produce several other DiskPulse versions that add more capabilities and features. They're able to monitor changes to specific file types, for instance; send email notifications of particular events; execute custom commands; produce HTML, CSV and text reports, and more. These commercial versions are priced from $25, and you can read more on the DiskPulse site.
Sysinternals tools like Process Monitor provide more details about exactly what's happening on your PC, but if you only want to monitor hard drive changes then DiskPulse is an easy-to-use way to get the job done