I have a Ubuntu file server and it makes the oddest sound. I can hear a HD making a "breathing" type sound, like the disc spins up for a moment and then cycles down. It happens on a very regular basis, about every 20 seconds or so. I've run every HD diagnostic I can think of, and I can't figure out what might be causing it.
The system runs Ubuntu 11.04, with a OS HD & 4 discs configured in a RAID5 array.
Is this something I should be worried about? Is there any utility I can run to see why the disc keeps spinning up?