Disk Chatter Windows 98

I am supporting a pc with windows 98 that starts to read the “c” drive every 10 or 15 minutes. You can here the disk working overtime for a few minutes and then it quites down. This all happens when the pc is not being used, just powered up. I have disabled Norton System Works stuff and Win98’s Maintenance Wizard tasks. I have looked for the offending task in the task manager to no avail. Your ideas would be appreciated. Gary