I've got a 1TB Fusion Drive (with a Seagate 7200 rpm hard drive) in a Late 2013 27" iMac. While the iMac is asleep, the hard drive spins up and down every minute or so (without fail), creating an annoying rattling sound as it spins up - characteristic of hard drives. This is incredibly annoying, especially at night.
It doesn't exhibit this behaviour when it is powered on, just when it is asleep. I've tried disabling Power Nap, and checking and unchecking "Automatically put hard disks to sleep when possible", all to no avail.
It sounds more like a software issue than a hardware issue, has anyone else experienced similar behaviour with the Fusion Drive?
Is there anything I can do to stop this? It's driving me crazy.