What was found
AIRCRAFT WAS GROUNDED: FA ADVISES SHORTLY AFTER TAKEOFF LOUD SQUEAL FROM L1 FORWARD ENT RY DOOR. NOICE SEEMED TO BE COMING FROM DOOR HINGE AREA. REPEAT WRITE UP. AIRCRAFT RETURNED TO ORD NO EMERGENCY DECLARED AND LANDED WITHOUT INCIDENT. MAINTENANCE WHILE INSPECTING THE DOOR FOUND L1 DOOR GUIDE ARM PIN HARDWARE MISSING AND INSTALLED NEW GUIDE ARM PIN ASSY, WASHER AND SCREW IAW AARD 52-10-00.