Does anybody know about a vibration that can be heard in the cab, which sounds a bit like wind noise against the roof rack, but it isn't as the roof rack has been removed but the noise remains. It occurs at 2000rpm to 3000rpm, I'm sure it's an engine issue but no one seems to be able to identify what it actually is. If clutch is depressed at 3000rpm, the noise dies with the engine, so it's not road noise either. Could it be a timing belt or alternator clutch...? Any ideas or any tests that I can do with the van to check would be gratefully received.

do you have a Dual mass Fly wheel ? hope its not that

yes it does have a dual mass fly wheel