I tried to get the lid off but the three pipes seem to be sealed to it. It's not my house, so I didn't want to monkey with that unless it was an emergency. All the plumbers around here are booked dealing with all the burst pipes, so we were kind of in a holding pattern. We left it unplugged overnight. Then the rain came this morning. Using a flashlight through the little hole in the lid I could see it's reflection in the water. Seemed like water was not coming in at all. It was low and there was no rippling despite the fact that it had been raining for awhile. I'd plug the pump back in and just the same steady humming with no apparent activity either in the sump or where the contractor said the discharge pipe is. I decided for the hell of it to tap on the pvc pipes with a hammer and just like that water came rushing into the reservoir, I could hear it going out the discharge pipe and then the pump shut off on it's own for the first time in days followed by the appropriate tapping of the check valve. It appears all has returned to normal. Based on what I've read online from others, it sounds like either it was air-locked, or maybe a combination of blocked intake pipe and stuck floater.
I wasn't aware of how high the water level gets in the reservoir before the pump kicks on. Scared the hell out of me when it started functioning again. Is that common?