Sorry, I should have been more complete in my information...
This drive was the SSD boot drive for a laptop I recently replaced. It's approximately 18 months old, maybe a bit less. It's a 250GB Samsung 840 EVO with the current firmware installed.
I plugged the drive into a Windows 10 Professional desktop to partition the drive and format it. I created a single partition approximately 220 GB and left 16 GB unallocated for over provisining, although I'm not sure that or TRIM will work with the drive in a USB port. Once the data was copied to the drive it was plugged into a USB 3.0 port on a hub connected to the laptop via the USB 3.1-c port. In that connection I got the behavior described.
I MOVED the drive to a "regular" USB 3.0 port on the laptop and the drive appears to behave normally. It no longer shows 100% activity all the time.
I presume there is some difference with a USB 3.0 port that's on a 3.1-c hub, but it's not a big issue since I can plug the SSD into a "normal" 3.0 port.
As for virus or other malware, it's certainly possible, but neither my antivirus, nor the Malwarebytes anti-Malware software has indicated any problems.
As for putting it internally, I wish I could! Unfortunately, the new laptop only has one internal drive bay that's occupied by a 1TB HDD and uses an M.2 SSD for a boot drive. Thus my thinking I may try the other SSD as an external drive for data that benefits from extremely fast access such as large digital images at the time of capture.
Anyhow, I'll do some testing and fiddling and if it works well, great. If not, I'll do without it.