Rear window on tailgate- opening by itself?

Ford Explorer 2002, the rear window on the tailgate keeps opening by itself. I was driving, came to a red light, stopped and the window just unlocked and opened. I pulled over- closed it and made sure it was closed tightly. Got home parked the vehicle and it did it again. Closed the window again tightly and locked all the doors using my key fibe. I then press the key fibe to unlock the window and then it makes a second click as if it's locking or unlocking again- only it can't lock or unlock because the window is now open. Not sure if that has anything to do with why the window was opening by itself but thought I'd mention it. Any ideas what could cause the window to open by itself. The only way to open the window is using the key fibe- no button or latch for it in the vehicle. Any advice will be much appreciated! Thanks in advance.

Added (1). Sorry key FOB - not key fibe.

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