periodic hdd sound. not a mechanic issue

as you can hear, there is a periodic (hard disk head scan)sound comes from my hdd (or one of the hdds) I have 2 hdd, 1 ssd. because of ssd, auto defrag is disabled. also windows index feature is disabled. current working apps are shown as an image. what could it be? sound: http://ift.tt/1KQ8xdA apps: http://ift.tt/1CZAlNd

bytheway, hd tune says "interface crc error count" error/warning, only. there is no bad problems in s.m.a.r.t.