Could not find any similar post here, so either I'm an idiot or everyone else already knew how to fix it, or just gave up.
Enclosure: MB561U3S-4SB R1
OS: Windows 10 PRO
PC: HP EliteBook (Business Notebook line)
Connection: USB UASP
When the PC goes to sleep or is powered off, drives in the IcyDock do not power off or even go quite. Instead they start cycling. It sounds like they are spinning up and down, over and over.
SOLUTION - HP BIOS Setting "Device Configurations" -> "USB Charging Port" (Allows an external device to charge until a specified battery charge level is reached) is ENABLED by default. Disable this and the IcyDock spins down the drives correctly.