On my 2004 Mercury Monterey the electric locks have started to randomly open and close. When parked, engine off, sometimes the right rear side door just opens up.

The door locks lock and unlock at seemingly random times while driving or while parked with the engine off. The right rear side door randomly opens, but does not close while the van is parked and the engine is off. This started a couple of days ago. I have other vehicles and used them. This morning the battery in the van was drained enough that I couldn't start it, though while I was seated in it there was a continuous sound of some solenoid attempting to operate from under the dash.