Mine has only done it a few times, about 3, but in all cases I had to reboot to get it to slow down and in all cases the drive was not in use.
I mostly use it for a backup to a DL4100 and different systems also do backups to it.
When the fan is high the first thing I do is look at the Processes running to determine if anything is running, and anyway you can tell from the noise level of the drives if anything is running.
If backups are running, then I don’t worry about the fan and it normally goes back down once activity dies down.
But if after activity stops I check the temperature on the drives and they are normal, then I wait a while and after a while, that’s when I get tired of the added noise and reboot.
i think there a bug there that under certain conditions, it doesn’t slow the fan down.
In case WD reads this. For Windows I map a share and use Norton Suite to do backup. Acronis 2018 also does backups to that drive.
I also have a MAC and use TimeMachine for backups to its own share. I also use Acronis 2018 on the MAC.
I use Beyond Compare 4 in Windows to Keep my critical shares backed-up from th DL4100 to the DL2100.
I’ll try to see if I can determine that last thing that ran when the fan stays running high.