A319 FLT CREW AT FL320 EXPERIENCES LIGHT TO MODERATE AIRFRAME VIBRATION DUE TO UNKNOWN CAUSES AND ELECTS TO DIVERT RATHER THAN CONTINUE OVER WATER TO DESTINATION.

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ENRTE WE ENCOUNTERED A LIGHT TO MODERATE AIRFRAME VIBRATION. SINCE THERE ARE NO ESTABLISHED PARAMETERS FOR VIBRATION AS THERE ARE FOR ICING OR TURB; I FELT THAT A LIGHT VIBRATION IS ONE THAT IS NOTICED BY MAINLY THE COCKPIT CREW OR CABIN CREW -- BUT NOT BOTH. THE NEXT STEP WOULD BE MODERATE VIBRATION NOTICED BY PAX/CABIN CREW AND COCKPIT CREW. SEVERE WOULD BE EVERYONE KNOWS AND IS SCARED. THE ENGS WERE INDICATING LESS THAN 1.1 UNITS OF VIBRATION AND WERE BEHAVING NORMALLY; SO WE RULED OUT THEIR CAUSE. THE VIBRATION WAS FELT AT FL320 WITH THE SPD AT .79. WE SLOWED TO .76 AND VIBRATION WAS NOT AS PRONOUNCED AT THE SLOWER AIRSPD; BUT STILL NOTICEABLE. WE DSNDED TO FL280 AND MAINTAINED .76 AND AGAIN NOTICED THE VIBRATION INTENSITY DECREASE; BUT IT WAS STILL APPARENT THERE; TOO. WE ESTABLISHED A COMRDO PATCH WITH DISPATCH; AND AFTER CONFERRING WITH FO; DECIDED THAT OUR BEST OPTION WAS TO DIVERT TO ZZZ1. EVEN THOUGH DISPATCH FELT WE COULD WRITE IT UP IN ZZZ WE BOTH FELT THAT AS WE MADE OUR WAY TO THE OCEANIC RTES; OUR OPTIONS WOULD BE FEWER IF THIS PROB WOULD MANIFEST ITSELF IN A MORE SEVERE OR DRAMATIC FASHION AS WITH THE MD80 WITH THE JACKSCREW. AS WE DSNDED TO THE LOWER ALTS; EG FL180; WE NOTICED THE VIBRATION WAS NO LONGER PRESENT. FLT ATTENDANTS ALSO NOTICED THE VIBRATION IN THE REAR OF ACFT. THE 'A' FLT ATTENDANT IN THE FRONT OF THE ACFT; DID NOT NOTICE ANY VIBRATION. WE LANDED IN ZZZ1 BELOW MAX LNDG WT WITHOUT FURTHER INCIDENT. WE CONTINUED ON TO ZZZ WITH ANOTHER ACFT. WE LOOKED FOR VIBRATION RPT FORMS IN THE ACFT AND IN THE MANUALS; BUT COULDN'T FIND ANY. PERHAPS IT WOULD BE A GOOD IDEA TO PRINT SOME FOR OUR PLT'S HANDBOOK OR FOM. I GRABBED AN EXTRA AND PUT IT IN MY FLT KIT.