It's not uncommon for things to be going on in the background of a Linux installation. It could have been locate refreshing it's database. Very rarely do I pay any attention to what's happening, disk activity wise, as long as the system is running smoothly. If things seem to run slowly, I'll check top to see what's using the resources, and possibly shut something down temporarily, until I finish my immediate tasks, but mostly I just let things run through whatever they are doing.
Stopping running processes that you think shouldn't be running, as often as not, causes problems later on. Over the years I've found things remain running more smoothly overall, if I let the system just finish whatever it wants to do.