The airplane was in cruise flight when a pronounced airframe vibration started. At the same time, the #2 engine thrust reverser armed light illuminated, but no other lights illuminated. The abnormal procedures check was initiated, the #2 throttle was moved to the idle position, and airspeed was reduced. A precautionary landing was accomplished at the departure airport. Examination of the airplane by company maintenance personnel revealed the right wing fixed trailing edge panel had separated and collided with the fore flap and inboard mid flap.