Why won't MyCloud just shut up?

Your screen shows the guilty app. wdmcserver is wd file photo indexer. It is well known hot mess. Turn it off as it kills performance.
See Disabling "wdphotodbmerger" and "wdcmserver"

Put it in cron so it does not startup after a boot.

The only functionally you loose are the file type percentages on the dashborad and photo thumbnails. And you gain HUGE performance and drive lifetime!!!