Daf cf with a vibration

Hi guys.just wondered if anyone had ever come across a problem I have with a daf cf 8x4 tipper.when in 5th and 6th gear under load the vehicle has a vibration.visually checked everything but can’t find anything that would cause this.Any help greatly appreciated.

Centre prop shaft bearing ?

peterm:
Centre prop shaft bearing ?

+1, sounds like propshaft or diff related. Do either of the diff lock switches (lights on dashboard) come on on their own? That was a warning that a diff was on its’ way out on an Alpha I used to drive.
Have you checked the rear wings? If you drive a muckshifter they’re often bolt ons and will work loose. Could be low speed vibration affecting them but more like prop related.