FLC OF A B727 DIVERTED TO LAND AFTER CABIN ATTENDANT ADVISED HEARING A LOUD NOISE FROM THE REAR SVC DOOR. THE FE NOTICED THAT THE ACFT WAS NOT PRESSURIZING DURING DEP CLB.

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FLT XXX WAS SCHEDULED BTWN SAN ANTONIO; TX; AND ATLANTA; GA. DURING THE TAXI OUT; ONE OF THE FLT ATTENDANTS IN THE REAR OF THE ACFT CALLED TO SAY THAT THE R AFT SVC DOOR WAS LOUDER THAN NORMAL AND I SENT MY SO BACK TO INVESTIGATE. HE RPTED TO ME THAT THE NOISE LEVEL ASSOCIATED WITH THE DOOR WAS ABOVE NORMAL BUT ALL INDICATIONS WERE THAT THE DOOR WAS CLOSED. WE CONTINUED THE TAXI AND TKOF AND SEVERAL MINS INTO THE FLT THE FLT ATTENDANT IN THE REAR AGAIN CALLED CONCERNING THE DOOR. MY SO AGAIN WENT BACK FOR A LOOK AND RPTED IT TO BE VERY LOUD NEAR THE DOOR. AS HE RETURNED TO THE FLT DECK IT BECAME APPARENT THAT THE CABIN WAS NOT PRESSURIZING NORMALLY AND WE WOULDN'T BE ABLE TO CONTINUE THE CLB. AT THE TIME; THE ACFT WAS AT 12000 FT AND WE GOT A CLRNC FIRST TO 10000 FT AND THEN DOWN TO 8000 FT. AFTER TALKING WITH OUR COMPANY DISPATCHER; WE DECIDED TO DEVIATE TO DFW WHERE OUR MAINT STAFF COULD LOOK AFTER THE ACFT. OUR LNDG REQUIRED APPROX 6000 LBS TO BE DUMPED TO GET DOWN TO OUR MAX LNDG WT. MAINT INFORMED ME THAT LOWER PART OF THE EXTERIOR OF THE DOOR HAD MISSED THE CAM AND HAD NOT CLOSED PROPERLY. THE ACFT WAS SVCED AND REDISPATCHED TO ATL.