AME1117;
I experienced airframe vibration a number of times on older A320's. The vibrations were about 6 to 8Hz and could be felt on a larger cycle of about 1 minute - about 20 seconds of vibration, 40 seconds of calm, and repeated, sometimes quite strongly, in the cockpit and through the thrust lever quadrant. I kept records in my log book and got a particularly bad airplane one day - climbing through about 270, Mach 0.76 and increasing, when the vibrations began. I asked my F/O to go back to see if anyone felt it in the cabin. He was a very sharp guy and returned about ten minutes later and said to me, "you have to go to the back of the airplane and look out". I did. I watched, as both horizontal stabilizers began fluttering up and down describing an arc of about 1 ft or so. They were fluttering at about 6 to 8Hz for about 20 seconds gradually damping then beginning again after about 40 seconds. The pattern did not vary with Mach or altitude. It would gradually stop after some time in cruise.
We'd been writing up airframe vibration for years. It was always dismissed as "gear doors", "flaps", "turbulence" etc.
I grounded our aircraft at the next station. I learned later that it was a known issue by Airbus and that another large US carrier had had experience and it was even written up in Airbus' larger "industry issues" publications they used to distribute. Why our maintenance people or flight ops people had so much trouble finding out what it was, was a mystery. The fix was as stated here - replace worn elevator bushings, and, using a special tool, bias the elevators "down" by half a degree (if I recall). The fleet problem disappeared overnight.
That's one experience. Hope it helps solve what you're looking for.