Allegedly, on or about 7 December 2017, Fulko Hew sent:
To disable the Advanced Power Management and to stop the head unload/clicking I've always used:
hdparm -B 255 /dev/sda
But on this machine/drive, it doesn't seem to work; or at least it only works for a short while, and then it starts unloading again.
Is there a laptop mode set somewhere? That'd be a conflicting configuration.
https://wiki.archlinux.org/index.php/Laptop_Mode_Tools