What was found
AFTER TAKEOFF FROM SMF, GEAR UPLATCH CHECK OK. AIRCRAFT HAD A VIBRATION WHICH SEEMED TO COME FROM THE NOSE. THE VIBRATION PROGRESSIVELY GOT WORSE, CYCLED GEAR SEVERAL TIMES AND LOUD POP WAS HEARD. VIBRATION AND NOISE WENT AWAY, DID FLY BY AT SMF AND GROUND REPORTED ALL GEAR DOORS IN PLACE. REPLACED LEFT FORWARD NOSE LANDING GEAR DOOR LINK. RIGGED AND OPS CHECKED GOOD IAW DC-8 MM 32-22-1.