What was found
SFO - CREW DESCRIBED POPPING SOUND COMING FROM THE FORWARD CABIN DOOR AREA. EMERGENCY DECLARED, RETURNED TO SFO WITHOUT INCIDENT. MAINTENANCE WAS ABLE TO DUPLICATE SOUND AND FOUND POPPING SOUND COMING FROM FORWARD EDGE OF LEFT NUMBER ONE DOOR AREA JUST FORWARD OF WINDOW ON THE DOOR. FOUND THERE WAS A PROBLEM WITH HOW THE DOOR CLOSED. REPLACED 13 OF 16 DOOR STOPS DUE TO UNUSUAL WEAR AND REPLACED THE ROD FOR THE AIRSTAIR INTERLOCK DUE TO IT BEING BROKEN. SYSTEM GROUND CHECKED NORMAL OPERATION.