I initially suspected the alternator, but I removed serpentine belt and han d-turned the alternator to inspect it. It turned smoothly without noise. No ne of the other pulleys seemed to be have bearing trouble either (although I'm not clear how to test them exactly).
The recording is from a simple Samsung Galaxy Centura cellphone, so the aud io low quality, but it does reveal the noise in question. (I'll try to edit it to eliminate the video element to reduce size. I apologize for now for the raw form.) The car currently functions fine except for the noise, which is audible a l ittle to me while driving.
I'm guessing the valves are in trouble, but I'm not sure, and I'm not sure what exactly would be wrong with them. And it still could be the alternator . Maybe (although it seems to turn silently unattached) the tension of the belt on the bearing will cause it to misbehave. What's my next step in dia gnosing this problem?