As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INTERMITTENT FLUTTER IN THE AIR-CONDITIONING AND PRESSURIZATION SYSTEM FOLLOWED BY PRESSURIZATION FLOW LIGHT. EMERGENCY DECLARED, RETURNED TO DEPARTURE LANDING UNEVENTFUL. REMOVED AND REPLACED TURBINE COOLING OUTLET DUCT AND ADJACENT FORWARD BOOT ON THE RIGHT ACM IAW AMM 21-20-15. LEAK AND OPS CHECKED GOOD. AIRCRAFT WAS GROUNDED.