What was found
DCA - FLT 360 - ON CLIMB-OUT FROM DCA, EN ROUTE TO ROC, CREW FELT A RUMBLE/AIRFRAME VIBRATION THROUGHOUT THE CABIN. DUE TO PREVIOUS FILGHT SEGMENT EXPERIENCING THE SAME PROBLEM, FLIGHT RETURNED TO FIELD AT DCA. FLIGHT LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE FOUND THE RIGHT ELEVATOR TRIM TAB INBOARD ATTACH FITTING BOLT AND BUSHING WORN. REMOVED AND REPLACED INBOARD ATTACH FITTING BOLT AND BUSHING FOR RIGHT ELEVATOR TRIM TAB. OPERATIONAL CHECK GOOD. (M)