AN AIRBUS A320 IN CLB AT FL280 ENCOUNTERED A MILD ELEVATOR VIBRATION CAUSED BY WORN ELEVATOR SERVOS.

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CLBING THROUGH FL280 AT 302 KIAS IN SMOOTH AIR; WE SUDDENLY EXPERIENCED A STRONG AIRFRAME VIBRATION. THIS DID NOT FEEL LIKE TURB. I TURNED ON THE SEAT BELT SIGN AND SLOWED TO 280 KIAS. VIBRATION STOPPED WHEN WE SLOWED THROUGH 290 KIAS. I CALLED THE THIRD FLT ATTENDANT AND SHE SAID SHE FELT VERY STRONG VIBRATION IN THE AFT CABIN. I CONSULTED WITH COMPANY MAINT CTL; AS OUR A320 FLEET HAS A HISTORY OF TAIL VIBRATION EVENTS. SINCE WE WERE NO LONGER EXPERIENCING VIBRATION AND MAINT AGREED IT WAS PRUDENT; I ELECTED TO CONTINUE ON TO CMH. I WROTE UP THE OCCURRENCE IN THE LOGBOOK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FLEET WAS PURCHASED USED AND WERE BUILT IN THE LOW 1990'S PERIOD AND IS EXHIBITING EVERYTHING FROM SEVERE FLUTTER TO MILD VIBRATION ON THE ELEVATOR. THE RPTR SAID THE FIX ON THIS AIRPLANE WAS REPLACEMENT OF THE ELEVATOR SERVOS. THE RPTR SAID THE COMPANY WAS SLOW TO MAKE THE NECESSARY CHANGES RECOMMENDED BY THE MANUFACTURER FOR THIS FLEET PROB. THE RPTR SAID THIS IS AN AGING ACFT PROB.