What was found
AFTER TAKEOFF AND GEAR RETRACTION, VIBRATION COULD BE FELT AND HEARD FROM NOSE GEAR AREA. ALL INDICATIONS WERE GOOD. RECYCLED GEAR THREE TIMES, ON THIRD TIME, VIBRATION CEASED. REPLACED DOOR BUMPERS, AND PERFORMED ADJUST/TEST IAW DC8 MM 32-20-00, NO DEFECTS NOTED.