AN ACR MD80 FLC RPT THAT THE GND CREW LEFT THE WATER SVC DOOR OPEN AND DURING FLT IT CAUSED VIBRATION AND NOISE IN THE CABIN AREA. THE FLC DIVERTED AND MADE AN OVERWT LNDG.

Narrative

DURING PREFLT OF ACFT; WATER SVC DOOR WAS OPEN WITH HOSE CONNECTED. DEPARTED SFO AT XA43Z. GND CREWMAN ADVISED ALL SECURE BELOW. REACHING CRUISE ALT I WAS INFORMED BY THE FLT ATTENDANTS THAT THERE WAS AN UNUSUAL TAPPING NOISE COMING FROM THE AREA AROUND SEAT XX. I SENT FO TO INVESTIGATE AND HE RETURNED WITH MORE INFO. AFTER A SHORT DISCUSSION ABOUT POSSIBLE CAUSES; I WENT TO INVESTIGATE. UPON MY RETURN; I CALLED MAINT AND CONSULTED WITH THEM. MAINT AND I BOTH THOUGHT IF THE DOOR WAS OPEN IT WOULD HAVE A HIGHER FREQ OF VIBRATION. I MADE 2 OR 3 MORE TRIPS TO THE CABIN AFTER TRYING NUMEROUS IDEAS FROM MAINT AND EACH TIME NOTHING CHANGED. WE THEN DECIDED TO SLOW THE ACFT TO 250 KTS AND THE VIBRATION QUIT ALMOST IMMEDIATELY. AT THIS TIME I DECIDED TO DIVERT TO SLC AS I THOUGHT THE WATER SVC DOOR WAS OPEN. WE LANDED AT SLC AT XC28Z AND TAXIED TO THE GATE. THERE IT WAS DISCOVERED THAT THE WATER SVC DOOR WAS COMPLETELY UNLATCHED WITH NO DAMAGE. THE OVERWT LNDG INSPECTION WAS COMPLETED; REFUELED; RELEASED AND DEPARTED FOR ORD.