As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
F/A REPORT LOUD NOISE IN AFT GALLEY ON INVESTIGATION HIGH PITCH WHINE COMING FROM BEHIND AFT GALLEY BULK HEAD. APU WAS RUNNING, SO PUT GROUND POWER ON ACFT, TURNED APU OFF AND LOUD NOISE WENT AWAY. DIMINISHING AS THE APU WOUND DOWN. ACFT GROUNDED. R & R APU REF AMM TASKS 49-11-00-000-803 AND AMM TASK 49-11-00-400-803 THROUGH STEP M.4. COMPLETED INSTALLATION OF APU REF AMM TASK 49-11-00-400/801. OPS AND LEAK CHECK SATISFACTORY.