Hi All, my vivaro was lacking power at low revs and was diagnosed with a mass air flow problem which I took to a garage to be replaced, once replaced the mechanic started the van up and it ran fine for about 15 seconds then the engine tone changed to what I can only describe as a bag of hammers being thrown around, as a process of elimination he changed the cam belt and pulleys, still no change, called the AA out again and they didnt know what it was so took the van to a 2nd garage, they were puzzled and suggested to change the mass air flow "AGAIN" but the noise was still there, so several people suggested to take it to a well known and very good diesel specialist which I did and after they investigated the following removed exhaust, air intake hose, egr valve, assy, turbo actuator, cambelt cover, auxilairy drive belt and air flow meter to try to identify where and why the van is making such a noise but to no avail. so far the van has as you can imagine cost a small fortune but it still sounds like a massey ferguson tractor. has anyone experienced this or do you know what it is ? please please help, many thanks and thanks for reading, regards allan.