AIRFRAME VIBRATION DURING CLB AND CRUISE.

Narrative

DURING CLB AND CRUISE WE RECEIVED CONTINUOUS LIGHT AIRFRAME VIBRATION. THE VIBRATION WOULD INCREASE AND DECREASE IN INTENSITY; BUT WAS NEARLY ALWAYS CONTINUOUS. EACH TIME THE INTENSITY INCREASED; WE PRESSED THE EVENT RECORD BUTTON ON THE DIGITAL FLT DATA RECORDER. THE VIBRATION SEEMED TO BE CONTINUOUS AT THE HEAVIER WTS AND WAS NOT NOTICEABLE AT THE LIGHTER WTS. IT SEEMED TO BE CTRED FROM THE WINGS AFT; EITHER IN THE AFT BODY OR THE TAIL. VIBRATION WAS VERY NOTICEABLE TO PAX AND CREW. I THINK THIS COULD BE A SERIOUS SAFETY PROB (POTENTIALLY) IF THIS IS ALLOWED TO CONTINUE. I FLEW THIS ACFT IN MAY AND LANDED SHORT OF OUR DEST DUE TO MODERATE TO SEVERE AIRFRAME VIBRATION. (I FILED A RPT THEN; TOO.) I CAN PERSONALLY DOCUMENT 10 SEPARATE WRITE-UPS ON AIRFRAME VIBRATIONS FOR THIS ACFT (2 BY ME). COPIES OF THE WRITE- UPS AND SIGNOFFS ARE AVAILABLE. I THINK WT MAY BE A FACTOR. I HAVE FLOWN THIS ACFT AT LIGHTER WTS WITH NO PROBS. MAINT USUALLY CANNOT DUPLICATE BECAUSE TEST FLTS ARE AT LOWER WTS. LIGHT TURB SOMETIMES STARTS THE VIBRATIONS. IN MY 2 VIBRATION INSTANCES WITH THIS ACFT; MAINT DID NOT PULL THE DIGITAL FLT DATA RECORDER.