WD6003FFBX high-pitched buzzing sounds when idle

I operate 4 new WD6003FFBX WD Red Pro drives in a NAS. Only when idle regularly one or more drives emit a strange, not normal sounding, high pitched, whining, buzzing noise I recorded here:

You can clearly hear the whining noise next to the normal hard disk drive sounds.

The whining sounds stop very quickly when I copy a larger file to the NAS or read a larger file from the NAS. After the copy process stops the whining noise continues.

The whining noise also comes and goes during idle state, so it is not there all the time the NAS is idle (just yet).

As it is high pitched and unregular, it is annoying and worrying. So I am now wondering if I should try to isolate the drive which makes these noises when this happens again by hot plugging one drive after the other and replace the dying drive or if this is somehow normal for a 6TB WD Red Pro or if this is a known issue and a firmware patch is in the making or available.

I would recommend you to run the system diagnostics on your NAS in order to find if there is any issue with the drives.

If you are using My Cloud NAS, you can click on the link given below to run system diagnostics.

Moreover, you can also run the full test on the drive from winDLG by connecting the drive with your computer through SATA port. You can refer the link given below to know about winDLG.

I have the same issue with my brand new PR4100 with 4 10TB Red drives. Has anyone found the cause?