As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#1566, SAT-BOS. (AIRCRAFT PERFORMED AN AIR TURN BACK TO SAT) DURING ALL PHASES OF FLIGHT LOUD BANG IN TURNS CLIMB, DESCENT. THE EVENT HAPPENED 10 TIMES OR MORE; ROUND NLG PINTLE PIN GREASE SERVICE POINT TO BE DRY AND LEAKING GREASE. PERFORMED NLG LUBRICATION IAW AMP BP500-A-512-20-32-01AAA-290BA.