I have some iMacs (running 10.5.6) each with an external direct-connect FireWire hard drive. About every ten minutes, these drives will spin up for a minute or two, then spin down again. I'd like to know why! Can anyone help to explain what is using the drives, or how I might check? Background: The drives are set as Time Machine backup volumes on their respective iMacs. I assume the frequent accesses I observer are not related to Time Machine (because the accesses are much more frequent than the hourly backup schedule). The drives are not remote-mounted anywhere. In System Preferences I have the check-box enabled to "put hard disks to sleep when possible." I am very tempted to turn that off, because I'm worried about the stress being caused by spinning up and down these drives multiple times per hour.