HiCustomerand welcome to JustAnswer,
It's very common for the rear window regulator to rust up and bind. This will cause a lot of strain to the rear window motor also. Moisture gets inside the door and rusts everything up to a point where I have seen the tailgate turn into swiss cheese.
What you will have to do is take the rear door panel off and inspect the window regulator, motor, window run, and channels for extension rust exposure.
Using the key, operate the window "down" and let me know if the window motor tries to operate.
I would recommend replacing both the motor and window regulator as a pair. The regulator binds up and causes the motor to overload itself and eventually burn out.