I have an Fiat Autotrail 2.8 D, W reg. Over last few years I have been getting a vibration that appears to be coming from the engine but shakes the whole Van. It only occurs on Motorways and used to happen rarely and not for very long, this summer we did 3,000 miles but had no trouble until we hit the M20 around Ashford and lasted 20 miles then stopped. The last three times I've used it it has lasted longer until it lasted almost all the time from Exeter to Tewksbury but stopped as soon as I got off the motorway and even at the same speeds 50/55 did not start again. At first ,in Germany, I thought it was the road surface and again in England but I asked my mechanic when he put a new gearbox in to check the engine mountings, fine. Any ideas, is it the drive shaft? is it just an old van, my mechanic doesn't seem to know except he feels the Van has years left in her. Please help.