We have a TEC 718ti MH and its great (normally) its built on a Transit long wheelbase chassis. We have just returned from 17 days in France and during this time its developed a terrible buzz/vibration, it happens above 50 MPH and usually on toll roads which we have mostly traveled on, it continues from this speed up. It does not happen all the time and not on all road surfaces and it stopped when it rained? I have dipped the clutch and coasted but it still continues. We have felt everything in the cab but can't pinpoint anything that's vibrating. By the way it did not come on at all coming up the from Dover to Nottingham!