The door moves on tracks - correct? If one of the tracks is plumb and horizontal (or level) and the othertrack "end" is slightly off in or out the door will drop off the track then jump back on. this could be causing the bang! check for the same width along the whole door track. cut a 1X2 to act as a gauge and check the bottom, center and top all the way to the end of the track. next check your limits. the door shuts down at the same place all the time. this indicates the stop limit has been reached and its adjustment is off a touch. door mechanisms make use of a mechanical limit for door travel and a current sensing relay that stops the door when a set current is over shot as in an object in the path of the door travel. the electric eyes should be mounted on the wooden track supports NOT the metal track. as the door moves the track also moves and if the eyes are mounted on the track they too will move. once their light path has been broken, THAT circuitry will take over and shut down the drive motor.