As with all its services, Apple offers no real troubleshooting when iCloud Drive synchronization stalls in macOS. Glenn Fleishman encountered a problem that took months to diagnose and fix. In the process, he went through the wringer of trying nearly everything suggested online, via Apple support, and from colleagues. In the end, the magic that fixed it was undisclosed engineers.

Source: Cloudy with a Chance of Insanity: Unsticking iCloud Drive – TidBITS

Reddit threadsters are suggesting that certain 5400rpm 8TB Western Digital drives are actually rotating faster, at 7200rpm, and using startup sound profiles to back up their claims. There are a group of reddit threads, like this one by u/sbjf, saying WD 8TB EMAZ and EZAZ drives, used in WD’s Elements and My Book external storage…

via What madness is this? WD 5400 rpm 8TB drives sound like faster 7200 rpm spinners — Blocks and Files