What was found
AFTER TAKEOFF, SEVERE VIBRATION FELT BELOW COCKPIT AFTER GEAR SELECTOR VALVE IN NEUTRAL. RECYCLED GEAR UP AND DOWN, VIBRATION REOCCURRED AFTER PLACING LEVER IN NEUTRAL. YELLOW NOSE GEAR DOOR LIGHT ILLUMINATED ON BOTH GEAR POSITION INDICATORS. RETURNED FOR NORMAL LANDING. REPLACED NOSE GEAR DOOR ACTUATOR IAW 32-31-16, PERFORMED TEST IAW 32-30-00 PAGE 501, OPS CHECKED GOOD. RELEASED TO SERVICE.