My mom has a 19" iMac Core Duo running Tiger. It's been fine up until lately, within the past month or so, when you can hear the hard disks spin down frequently. It does not occur when the computer is in use, but after it's idle, it happens a lot. Sometimes every five minutes, sometimes every 15 minutes. It just seems to be too frequent. I have posted a screenshot of the Energy Saver control panel. Any thoughts? Is this a bad sign?