What was found
AFTER COMPLETEING A MISSED APPROACH AND RETRACTING THE GEAR, FLAPS AND LANDING LIGHTS, WE EXPERINCIED A PERODIC VIBRATION THAT WOULD LAST 5-15 SEC AND WAS AUDIBLE. WE COULD NOT DETERMINE ITS ORIGIN. JACKED AND SWUNG GEAR MAINS AND NOSE, INSPECTED DOORS FOR SECURITY AND DAMAGE IAW MM 32-00-00. HAD QUESTION ON PLAY W/MAIN GEAR DRS. THIS IS NORMAL COND ALSO EXTENED FLAPS AND INSPECTED. CHECKED LANDING LIGHTS FOR SECURITY AND DAMAGE--NONE FOUND. INSPECTED FILLET PANELS AND ANTENNAS FOR SECURITY. ALSO CHECKED HORIZ STAB CALLED TECH SERVICE, IF SMALL PLAY IS NORMAL. RESPONSE YES SMALL PLAY NORMAL . ALL CHECKS NORMAL NO FAULTS FOUND.