As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, THE FLIGHT CREW HEARD A LOUD SLAPPING NOISE BY THE FORWARD GALLEY SERVICE DOOR, PRESSURIZATION WAS NORMAL. RETURNED TO MSP WITHOUT FURHTER INCIDENT. FOUND THE FORWARD GALLEY SERVICE DOOR SEAL OUT OF ITS RETAINER AT THE UPPER FORWARD CORNER. DEFERRED THE REPAIR.