I forgot what the process was I had to kill. After about an hour, it was consuming 6.8 GB of RAM and 2 GB of swap. I think it was mate-settings-daemon something. Just checked, it's back up with 600 MB of RAM and upwards of 80% of CPU.
LMDE 64-bit Mate edition
Not sure how to find my hardware settings. System profiler is not present in Software Manager.
^What happens when I kill it.
I was trying to back up the files in my home directory (literally just copy and paste them) to a 1 TB HD, using a USB 3.0 connection. The external HD is 3.0 compatible.
This is what it normally looks like:
My other issue is that my laptop doesn't boot about half the time. Sometimes it will boot to grub, then the screen goes black and it never finishes loading Mint. I turned off Secure Boot and enabled Legacy Boot in the Bios before I installed Mint, and I can post my partition settings if you need it. This is really annoying, but not as much of an issue as the apparent memory leak.