As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PRESSURIZATION CHECK, A LOUD NOISE WAS HEARD FROM APU AIR INLET. ACFT GROUNDED. ACCOMPLISHED CHECK OF APU AND ACFT WIRING AND RESISTANCE CHECKS OF SAME. REF FIM TASK 49-70, TASK 806. ALL CHECKED OK. REPLACED DATA MEMORY MODULE. INSTALLATION TEST PASSES. NO CURRENT STATUS FAILURES. REF AMM 49-72-11/401.