As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURN BACK, EXPERIENCED LOUD BANGING NOISE SHORTLY AFTER LEVELING OFF AT FL400. INITIAL INSPECTION FOUND THE NR 1 PACK FWD & AFT RAM AIR DOORS DAMAGED. FURTHER INSPECTION FOUND 2 CRACKS TO THE RAM AIR INLET DUCT MEASURING 0.375 INCH LONG. TIME LIMITED REPAIR TO THE DUCT ACCOMPLISHED IAW SRM 51-10-02-0G-0. EO 4421A096 PART 1 DOCUMENTS THE REPAIR.