AFTER AN UNUSUAL NOISE DURING CLB FROM SFO THAT THE FLT CREW OF A B767 AND FLT ATTENDANT COULD NOT IDENTIFY; THE CREW IS TOLD BY GND CREW AT DEST ARPT; JFK; THAT THEIR HYD SVC PANEL HAD COME OFF.

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PASSING FL200 ON DEP FROM SFO WE HEARD A STRANGE SOUND (SIMILAR TO WHAT THE LNDG GEAR MAKES AS IT FINISHES RETRACTING). NO ABNORMAL INDICATIONS WERE NOTED; AND FO (WHO WAS HAND-FLYING THE ACFT) NOTED THAT IT CONTINUED TO FLY NORMALLY. SEVERAL MINS LATER THE FLT ATTENDANTS CALLED TO ASK IF WE HAD HEARD ANYTHING UNUSUAL AND WE TOLD THEM WE HAD. AS WE HAD NO ABNORMAL INDICATIONS; I ASKED THEM TO JUST KEEP US ABREAST IF THEY WERE TO HEAR OR FEEL ANYTHING ELSE UNUSUAL. PERSONALLY; IT SEEMED TO ME LIKE A CARGO SHIFT. #1 FLT ATTENDANT CALLED ABOUT 1 1/2 HRS OUT FROM LNDG WITH SOME WRITE-UPS AND MENTIONED THAT IT DID SEEM A BIT NOISIER AROUND ROW 30; AND I ASSURED HIM WE WOULD CHK IT OUT AT THE GATE. UPON ARRIVING AT GATE AT JFK A RAMP WORKER CAME UP TO THE COCKPIT TO TELL US A PANEL WAS MISSING. UPON INSPECTION WE FOUND THE HYD SVC PANEL MISSING WITH 2 ADJACENT FAIRING PANELS WITH A FEW SMALL PUNCTURES. SUPPLEMENTAL INFO FROM ACN 590188: THE HYD SVC PANEL UNDER PLANE AFT OF R WING WAS RIPPED OFF AND 2 OTHER PANELS WERE DINGED.