DS412+ constant disk activity

[nitraw]

I recently purchased a ds412+ and I like it very much apart from one issue:
There seems to be no pause to disk activity. I tried deactivating all installed packages and activating hibernation debug logging but it does not show any file operations for > 10mins (but the disks don't go into hibernation).

I also read that my disks are supposed to be quite quiet, but the noise is clearly audible from aproximately 3m / 10ft away (disks are 3x 3TB Hitachi HDS5C3030ALA630) so constant disk activity is really quite annoying.
I would appreciate any help on either one of these problems because it is the combination of those two that really irritate me.

What I also just noticed is that my load average is >2 but the cpu is (almost) idle (>98% idle in top), same as here: http://forum.synology.com/enu/viewtopic.php?f=19&t=55227