As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT ATTENDANT REPORTS LOUD BANGING IN AFT GALLEY DOOR DURING S.E. TAXI WITH APU RUNNING. GROUNDED - YES. VERIFIED LOUD BANGING SOUND COMING FROM APU WHEN HIGHER BLEED AIR IS REQUIRED (HIGHER THAN 20 PSI). NO DEFECTS IN TAIL PIPE. REPLACED APU ENGINE WIRE HARNESS REF B737-900 AMM 49-11-01. OPS TEST GOOD. LEAK CHECK GOOD.