I understand normal noise from a WD Red hard drive.
But I have an 8TB WD RED Plus and it makes a metallic sounding noise. You don’t hear it all the time, but you do sometimes and it’s outside the normal noise of a hard drive. It sounds like a vibration.
In the audio that I leave you it is heard in the second 00:09 to 00:11. Then it is heard at 00:45, 00:52, 00:57 to 00:58.
It is like a metallic membrane. I have disconnected the hard drive from the NAS and put it back but that sound sometimes does and I don’t know if you have encountered it before.