I recently noticed that my hard drive keeps running for no apparent reason. It does not actually run continually, it runs for about two seconds, stops, then, at a variable interval of five to fifteen seconds, it runs again. This is a lot of running to get nowhere. I tried shutting down all applications other than those running all the time by default (no browsers, file managers, or e-mail), and this made no change. Rebooting makes no difference.
It may be that I have set some program or service to run that I do not realize. Can someone help me to diagnose what is happening?