My Passport 4TB drives no longer spin down when idle in Win10 Pro

I have two identical My Passport 4TB drives attached to my newly-built Intel i7 Win10 Pro (1909 update) machine, P/N starting with WDBYFT. They’re left connected/powered 24/7 for use with Acronis to do a daily backup.

Initially, both drives would spin down and go into Sleep mode after a few minutes idle, but they no longer do so, spinning all the time now, so I’m concerned about excessive heat and wear. I can see the drive activity light flashing every now and then, so something seems to be pinging the drives and keeping them awake.

Any ideas for the right tools I can use to track down the culprit? I’ve checked Windows power settings and Disk Management policies are currently set to Quick Removal, no write caching.