@gekco, welcome to the club of unknown.
There are threads here in this forum with same problem and no answers.
Check this links:
https://community.wd.com/t/when-hdd-power-off-it-makes-moaning-noise/218183
https://community.wd.com/t/wd2005fbyz-noise-when-pc-is-power-off/215513
https://community.wd.com/t/wd-black-spin-down-noise/198722
I know that this is not an answer to your problem, but sincerely I lost hope to hear at-least some explanations from a WD technician …
