Welp, turns out the playing AC overwhelmed my computer's default cooling system.
So, stuck in noisy fan, and all is right again with the world.
I can definitely endorse the Silverstone 'Air Penetrator' series for solving these kinds of problems, though it is really noisy.
I wonder when someone will make a decent fan that can do low RPMs, but can also do high RPMs. *shrug*. Oh well.