I can't get my rear windows to go up or down. The motors are ok, I have checked with an external power source. There is power to the windows, I have checked the fuses, I have checked continuity on the switches. When I press the button, I hear a faint click or whine, but the windows do not move. Every so often (about 1% of the time) the window does move ever so slightly, either up or down, but not enough to close them or open them.