There is a vast SIL about airframe vibration which ends with a vibration reporting proforma. Using the proforma your clever people in engineering are able to isolate the problem, usually quite quickly. In the company I worked for there was a copy or two on the flight deck, usually in the documents folder. Being retired now I can't give you the SIL number but your engineers should be aware of it and be able to supply a copy of the fault finding proforma. Not much of an engineering department if they can't !