Continuous seeking noise from idle F2-210 with Seagate ST4000VN00802DR166 drives

[dmderev]

I experience continuous seek-like noise from TNAS when it is idle, the disk activity LEDs are not blinking for already several days. Since I had iFire ransomware attack on this box which encrypted all files recently, I am now paying extreme attention to any unusual un-advertised activity which does not have any explanation.
Did anyone experience such behavior?

This noise disappears and is replaced by regular seek noise when the data is being written or read, and the activity LEDs are blinking.

Questions:
1. Are there any processes that access disks but do not show activity on LEDs?
2. There are some topics suggesting that the sounds may be caused by synchronizing the drives in RAID1 pool. The NAS was powered for quite a while, and all synchronization was supposed to finish. Could somebody elaborate on details of what and when is happening when the NAS is idle?
3. The "synchronization" operations - are they supposed to show activity with the LEDs?

I know that the LEDs are not directly connected to drive or disk controller, because in older TOS they were not showing any activity at all. But in the latest TOS? It will be too bad if any disk activity stays hidden from indicators...

F2-210 TOS 4.2.43-

[dmderev]

P.S. The seek sound disappears when I start test for bad blocks. The LEDs are blinking at that time.

[dmderev]

The head activity continues all the time with no LED blinking. There is no log report on the disk activity, the drives are listed as healthy with no additional information. I ran scan for bad blocks - during the scan the annoying sounds disappear. Scan takes a long time, so I logged out. Surprisingly, when I logged in, I could not find any traces of the result of the scan in the log or anywhere (poor software design). After the scan, the annoying sounds continued again with no LED activity blinking.
I see two processes using 10.6% CPU - ksoftirq/0 (5.3%) and syscontrol (5.3%). What are these processes doing and how they are related with continuous drive activity?

[TMroy]

Please check on "Control panel > storage > storage pool", if the RAID 1 pool is syncing, if yes, you need to wait for the process to complete. If you installed big drives in your RAID 1 pool, the sync process could last for days.