What was found
DURING CLIMBOUT, A LOUD THUMP WAS EMITTED FROM NOSE WHEEL AREA FOLLOWED BY A CONTINUOUS VIBRATION. NOSE AND VIBRATION REDUCED UPON LANDING GEAR EXTENSION. AIRCRAFT RETURNED TO ORIGINATION AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE BYPASS HANDLE ACTUATOR, LEFT NOSE LANDING GEAR DOOR, CABLE, AND SPRING, OPERATIONAL CHECK OK.