Other symptoms: slow CPU without showing anything taking an inordinate amount of cycles, or 600%+ cycles taken by kernel_task, as measured by Activity Monitor.
I tracked down the origin of the problem: the $8 hard drive caddy was a little too thick, and it was causing the wifi connector to come off. (Backstory: I took out the optical drive a few months ago and added a 1TB HDD using this caddy.)
So now my 1TB drive is back out of my MBP, grrr. I'll use it externally until I find a remedy. I'm thinking just tape to keep that connection down.








