THANKS everyone for the responses about my radiator fan coming on....
I'm pleased (and embarrassed!) to report that it WAS my A/C switch.  We
had the car detailed last week, and they must have turned the knob, but
it LOOKED like it was off because the knob isn't on "straight".  I
turned the key, rotated the knob, and the fan went off.

Sorry to have taken your time on this little thing!

Emily