As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW NOTED 2 MINUTES INTO FLIGHT, HEARD A FLAPPING NOISE COMING FROM THE SERVICE DOOR AREA. THE CAPT DECLARED AN EMERGENCY AND WENT TO ORD FOR MTX. LANDED WITHOUT INCIDENT. NO OVERWEIGHT LANDING. REMOVED AND RE-INSTALLED SVC DOOR PROTECTIVE PLATE IAW EMB 145 AMM 53-21-13. THIS PLATE WAS LOOSE AND CAUSED FLAPPING SOUND. AIRCRAFT RETURNED TO SERVICE.