Why does the Terminal keep showing "^[[2~" randomly?
With a bit of trial and error, on my system I found that the Insert is ^[[2~. You can check this in a terminal by pressing CtrlV (to turn on Verbatim mode), then pressing Insert. It's possible the key is faulty and sending in keypresses randomly. I have heard of programs which inhibit sleep by simulating keypresses (perhaps Caffeine?) so that might also be a cause.