As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON STARTING LEFT ENGINE, LOUD RUMBLING NOISE AND HEAVY VIBRATION FELT IN CABIN. RAN NUMEROUS DIAGNOSTIC TESTS ON LT ENGINE. NO ENGINE PROBLEM NOTED. DURING DRY MOTORING, AIR SURGES THROUGH ENG CORE, SIMILAR TO PREVIOUS APU SURGE CONTROL VALVE FAULT, ACCOMPLISHED NR 2 ENG START. ACCOMPLISHED DUAL ENG START FROM OUTSIDE AIR SOURCE, UNABLE TO DUPLICATE PROBLEM. ALL OPS NORMAL.