What was found
(CAN) PILOT REPORTED A CLACKING NOISE IN FLIGHT COMING FROM THE INSTRUMENT PANEL. DURING TROUBLESHOOTING THE INTERNAL BY PASS DOOR WAS FOUND INOP. IN THE CLOSED POSITION. FURTHER INVESTIGATION REVEALED AN INTERNAL FAILURE AS THE STOP BUTTON THAT ACTUATES THE INTERNAL LIMIT MICRO SWITCH HAD FALLEN OUT OF PLACE. THUS ALLOWING THE ACTUATOR TO GO BEYOND THE ALLOWABLE LIMITS. THE ACTUATOR HAD COMPLETELY UNSCREWED ITSELF FROM THE LINEAR PORTION AND UNDER LOAD WOULD HAVE CONTINUED TO OPERATE AND CAUSE A THUMPING SOUND UNTIL THE MOTOR FAILED.