What was found
DURING TAKEOFF, THERE WAS A LOUD BANG AND SEVERE VIBRATION. DUMPED FUEL AND RETURNED TO DEN. *S/D* ACCOMPLISHED CHECK OF AIRCRAFT FOR DAMAGE DUE TO EXCESSIVE VIBRATION FROM NOSE GEAR SHIMMY AND CHECK FOR SOURCE OF ABNORMAL NOISE. NO DEFECTS NOTED ON GROUND. AS PRECAUTION REPLACED BOTH NOSE GEAR TIRE AND WHEEL ASSYS PER MAINTENANCE MANUAL AND LUBED NOSE GEAR. ACCOMPLISHED NOSE GEAR EXTENSION AND RETRACTION TEST PER MAINTENANCE MANUAL. NO DEFECTS NOTED. ENGINEERING NOTE: AS OF JULY 7,1999, 35 FLIGHTS HAVE OCCURRED SINCE THIS INCIDENT WITH NO FURTHER WRITE-UPS FOR ABNORMAL NOISE OR VIBRATION.