What is this sound? Van won't start

Okay the other day I looked down at the temperature gauge and it was overheated so I turned it off. Let it cool off then turn it back on. Got home and there was a humming noise that was going on. I thought it was just the fan cooling the engine off when I got to the house. Well apparently whatever this humming noise is continued all night long completely killed my battery and now I've charged up the battery. Tried two different batteries and it will not start. I thought maybe it was a fan stuck on but I don't see the fan moving at all. It starts as soon as I hook up the battery, Even without the key in the ignition. It seems to be coming from below the battery. Maybe Fan's not moving. I uploaded a video so you can see what I'm talking about. If you have any any idea what I should check I'd appreciate it.