Hi, I have just read your message about your Vivaro makin a knocking noise. I have the same problem with my vivaro which started whenI had the mass air flow meter changed, due to lack of power. IT NOW SOUNDS LIKE A BAG OF HAMMERS BEING THROWN AROUND. The van has been to FOUR different garages and been looked at by two AA men. I reckon at least 10 mechanics have looked and listened to it and they are all baffled as to what it is. So far apart from the mass air flow being changed i have had the following work done as suggested as a process of elimination, "new cam belt and pulleys, disconected exhaust and air intake, EGR valve, assy, turbo actuator, auxilary drive belt and ANOTHER MASS AIR FLOW METER at great expense and the van sounds like a massey ferguson tractor. If you have managed to get yours rectified please please please tell me what it was, many thanks Allan.