B747 FLT CREW IS INFORMED DURING TAXI OUT OF A LOOSE PANEL NEAR NOSE. ARPT PERSONNEL ARE UNABLE TO LOCATE PROBLEM PANEL. ACFT ARRIVES AT DEST AND FLT CREW DISCOVER LEFT PACK DOOR HAS DEPARTED ACFT ENROUTE.

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DURING TAXI OUT FOR TKOF; GND CTL ADVISED US TO CALL OPS BECAUSE AN INBOUND TAXIING ACFT HAD RPTED A PANEL LOOSE ON OUR ACFT SOMEWHERE JUST AFT OT THE NOSE GEAR ON THE L SIDE. I CALLED OPS WHILE THE PNF TALKED TO GND. WHILE OPS HAD ME STAND BY; THE PNF HAD GND SEND AN ARPT SAFETY TRUCK TO VISUALLY CHK THE ACFT. OPS THEN ADVISED US OF THE SAME (AN INBOUND COMPANY ACFT THOUGHT THEY HAD NOTICED A LOOSE PANEL ON OUR AIRCRAFT ON L SIDE BEHIND NOSE GEAR). AN ARPT SAFETY TRUCK APCHED THE ACFT AND THE PNF WAS ABLE TO RELAY A REQUEST TO LOOK FOR A LOOSE PANEL ON THE L SIDE BEHIND THE NOSE GEAR. THE TRUCK DROVE TO THAT LOCATION AND VISUALLY INSPECTED THE ACFT. THE TRUCK THEN DROVE TO THE FRONT OF THE ACFT AND PARKED ON THE ACCESS ROAD. THE ARPT SAFETY PERSONNEL THEN GAVE US A THUMBS UP AND TOLD US ON THE RADIO HE HAD SEEN NOTHING LOOSE OR OUT OF THE ORDINARY. WE RELAYED THIS TO GND AND OPS AND CONTINUED TO TAXI FOR TKOF. AFTER BEING AIRBORNE ABOUT 6 HRS; THE 'A' FLT ATTENDANT RPTED A LOUD NOISE AND VIBRATION COMING FROM BELOW THE ACFT AT ABOUT THE WING ROOT ON THE L SIDE. WE TRIED TO ISOLATE THE NOISE BY TURNING OFF THE GASPER FAN AND AN AIR CONDITIONING PACK 1 AT A TIME WITH NO SUCCESS. ALL SWITCHES WERE PLACED BACK TO NORMAL. UPON TAXIING IN AT DEST; THE MAINT PERSONNEL INFORMED US THAT THE L AIR CONDITIONING DOOR HAD SEPARATED THE ACFT AND WAS MISSING. SUPPLEMENTAL INFO FROM ACN 797730: JUST AS WE APCHED ABEAM THE TKOF POS WE WERE NOTIFIED BY TWR TO CONTACT MAINT. WE COMPLIED AND WERE NOTIFIED THAT AN INBOUND ACFT HAD NOTICED A PANEL LOOSE OR HANGING NEAR THE L SIDE OF THE NOSE GEAR AREA. WE; AS A CREW; WERE PUZZLED OVER THE LOCATION BECAUSE WE KNEW THERE WEREN'T PANELS IN THAT VICINITY EXCEPT THE E&E DOOR. WE ADVISED TWR THAT WE NEEDED A VISUAL CHK; AND TWR TOLD US TO COME UP ON A DISCRETE FREQ; WHICH WE DID. ABOUT THAT TIME AN ARPT TRUCK APCHED FROM THE R AND WE ESTABLISHED RADIO CONTACT WITH HIM; EXPLAINING THE SITUATION. THE DRIVER OF THE VEHICLE PARKED NEARBY THE NOSE AND WALKED OVER TOWARDS THE NOSE AREA AND APPEARED BACK IN VIEW ABOUT 30 SECONDS LATER. HE GOT BACK INTO THE TRUCK AND GAVE US A THUMBS UP AND CONFIRMATION OVER THE RADIO THAT NO PANELS WERE VISUALLY UNLATCHED OR HANGING. WE THEN WENT BACK TO TWR AND ADVISED THEM THAT WE WERE READY TO DEPART. DURING CLBOUT AND CRUISE; NO NOISES OR VIBRATIONS WERE NOTICED BY US. HOWEVER; THE FLT ATTENDANTS IN THE REAR DID ADVISE US DURING CRUISE THAT THEY WERE GETTING A STRANGE NOISE FROM AMIDSHIPS. UPON LNDG AT DEST; MAINT CAME UP TO THE COCKPIT AND ADVISED US THAT A PANEL WAS MISSING. IT REMAINS A MYSTERY AS TO WHY THE PROPER LOCATION OF THE PANEL OBSERVED BY THE INBOARD ACFT WASN'T COMMUNICATED TO US. I ALSO WONDER WHY THE ARPT MAINT GUY DIDN'T NOTICE THE LOOSE PANEL WHILE HAVING A CLR VIEW DOWN THE LENGTH OF THE UNDERBELLY OF THE ACFT.