As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN OPERATING LEFT PACK ONLY ON APU BLEED AIR AND RH PACK ON RH ENG BLEED AIR F/A'S REPORT A LOUD THUMPING NOISE. NOISE NOT PRESENT WHEN APU BLEED SELECTED OFF. ( APU BLEED AIR SYSTEM; APU NOT OPERATED ) - - PERFORMED FIM TASKS 21-51 TASK 802 AND 49-55 TASK 809. NO FAULTS WITH DUCT PRESSURE / APU BLEED SOURCE. NO ABNORMAL NOISES FOUND. THIS CLEARS MEL 49-7-1 MDDR # 128602