Try this when dark. When using the window switch(es) for the back window, see if the dome light appears to go dim. If so, the window motor is in a bind and needs to be hit on the window motor housing. Sometimes CRC556 or WD40 can be sprayed on to the window motor through the belt weather strip area and that might loosen the motor otherwise the upholstery panel will have to be removed to access the motor area. Hint: in as must that the rear electric windows are seldom used, the windows should be checked for up and down operation at least twice a month.
