Once had experienced this on an old 320 in BA (an ex Caledonion) during the climb. Quite shook me up to be honest and I reduced the airspeed until the vibration disappeared. I spoke to a couple of ground Engineers on arrival who explained that such vibration was 'normal' on these aircraft.
I've never experienced such a phenomenon on any other aircraft in 34 years of flying and I don't wish to experience it again.
Regards
Exeng