As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HEARD & FELT LOW FREQUENCY RUMBLE. NO PRESSURE DIFFERENCES OFF ENGINE BLEED AIR. CPC 2 SYS IN CHARGE. REPLACED AVIONICS DUCT PER AMM. PRESSURIZED ALL DUCTS AND CHECKED FOR ADDITIONAL LEAKS -NONE FOUND. PERFORMED AVIONICS EQUIPMENT VENTILATION ADJUSTMENT AND TEST PER AMM, OPS CHECKED GOOD.