While cooking dinner,
A bit of looking around online, and I found a parts guide for it, showing the fan and how it fit into the back of the freezer (on this site called YouserGuide, which seems remarkably useful for things where the company hasn't seen fit to put this sort of thing online themselves). It seemed simple enough, and I figured that if I poked at the motor I might be able to determine if it was indeed broken -- simplifying the call to get it repaired -- or maybe even unstick it enough to get it to work a bit longer, if the bearing had gone bad as I was guessing from the earlier sound. So, I unloaded the still-frozen food into a dense pile in the fridge, and got to work disassembling the back of the freezer -- after unplugging it, of course. Two unscrewed screws later, and I was looking at the fan.
"Aha!" I said.
It turns out the motor was perfectly fine -- but the freezer had been building up ice from condensation, and one of the places it had been building up ice was inside the fan housing. (It had also been building up ice blocking the air channel down into the fridge, which was probably also not good for things.) The noise had been the fan hitting the ice, and then the ice built up a little more and the fan stopped turning entirely -- luckily right next to sub-zero freezer coils, so it hopefully didn't get damaged from overheating as stalled motors often do. That was easily cleared out, and I reassembled the freezer and plugged it in, and was very happy to find that, indeed, the fan was now working and blowing cold air into the freezer and into the fridge.
And, after putting the food back in the freezer, that was that.