What was found
FLT 280, PBI-BOS. RETURNED TO FIELD. ABNORMAL AIRFRAME VIBRATION ON CLIMBOUT THROUGH FL250 UP TO LEVEL OFF AT FL310. ENGINE 2 N1 VIB 1.8, ENGINE 1 N1 BIV .4. FELT MORE LIKE FLT CONTROL FLUTTERING. NO ABNORMAL ECAMS. HYD, FLT CONTROLS READ NORMAL. SUPPLEMENTAL INFORMATION TO FOLLOW.