It's not a hibernation issue, it's a fan speed issue.
If you set it to Auto: Off/Low/High, the fan seems to stick on High, no matter the temp, no matter the hibernation state of the drives. My desktop is right next to the unit, so I can hear when the drives go to sleep or wake from sleep (also noted by the lethargic response on a network share as they first come out of hibernate).
If you set it to Auto: Low/High, you can hear the fan speed change as it gets cooler or hotter.