Check if your Elements enclosure has an SMR drive inside.
If so, then it’s probably normal behavior (WD is reluctant in providing information on this topic). The cache flushing and zoned block rewriting an SMR disk needs, can only be done when the drive is idle and can go on for 40 minutes especially when you filled up the disk to the brink as DVRs tend to do with their disks, then a large cache of postponed block rewriting (probably loads of 256MB shingled blocks, but again no information from WD on this topic) becomes imminent and performance is down the drain and your drive will be very active whilst idle from the PC side. What happens when you unplug the power in this state is a mystery (again no information from WD on this topic).
Read up on this and this topic.
Your new drive will do the same in the same circumstances.
