said by IowaCowboy:Check every appliance, a high bill could be a sign of a malfunctioning appliance.
Found it! I just came back inside - it was definitely the sump pump. I have an outdoor sump pit next to the inground pool, designed to keep the water pressure from pushing too hard on the liner.
Anyway, the net net is that I just opened the lid of the pit and the motor is stuck and overheating. It was steaming inside the sump pit!
I just shut it off and I'll deal with it when it warms up. It's 6 degrees out there right now - mucho frio!
Well, that $75 motor just cost me about $300 in electricity. How fun.