ORIGINAL: PilotLight
Try pushing on the wires on the tail motor. Mine became loose inside the motor. The contacts to the stator were not as tight as when I first got it. Pushing on the wires caused the motor to increase lots of RPM. I used glue on the wires to hold them in place until the motor gets used up and eventually replaced.
Didn't last more than a couple flights. Had to order new tail motors.