What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: DURING CLIMBING, THERE WAS A LARGE POP FROM THE FRONT SERVICE DOOR. AT THAT POINT, THERE WAS A LARGE NOISE FROM THE DOOR, AND A PIECE OF THE HANDLE WAS VISIBLE FROM THE WINDOW. PRESSURIZATION WAS HOLDING, BUT IT FELT LIKE MASSIVE BUMPS IN THE SYSTEM. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT ORD.