What was found
DURING CLIMB OUT AFTER GEAR RETRACTION AT A BOUGHT 8,000 FT, BEGAN HEARING A THUD NOISE COMING FROM NOISE AREA OF ACFT. LOWERED MLG & NOISE WENT AWAY, NOISE CAME BACK AFTER RETRACTED. MLG F/O NOTICED SLIGHT YAW MOTION AFTER LOWERING MLG FOR LANDING NOISE DID NOT RETURN, F/O WAS ABLE TO FEEL A THUMB IN THE FLOOR WHILE ACFT WAS MAKING THUD NOISE. ACFT REMOVED FROM SERVICE. INSPECTED MLG & MLG DOOR ASSY INSP NLG & NLG DOOR ASSY, NO ABNORMALITY FOUND IAW AMM 32-20-00, & 32-21-03, 32-10-00. CLEANED ELEC CONNECTORS ON NLG SELECTOR VALVE & NLG DOOR SELECTOR VALVE. PERFORMED MULTIPLE NLG SWINGS. NO THUMP DETECTED & OPS CHECK GOOD AT THIS TIME. INSTALLED GEAR PIN FLAGS REF ESPM. 20-17 & AMM 32-30.