A more common cause of airframe vibration (which has been reported as aileron flutter, elevator flutter, and rudder flutter) is the wing to body fairings above the mid section of the wings. The rubber seals get distorted and start to allow air under the fairings and cause quite a loud and tactile vibration that has driven many technicians nuts. If you see a 320 with speed tape along the top seal of the fairing panel this is usually the reason.
I was skeptical until I saw a few chronic vibrators "fixed" with the speed tape.