4wd noise

I'm having trouble finding a noise in a 96 full time 4wd hiace.
It's a resonance kind of noise that happens at a specific Rev range in all gears, it seems to be amplified through the body work. It's driving me nuts and makes the van really unpleasant to drive for any distance. Have checked all the usual stuff, Any ideas appreciated, my last choice is the main input bearing of the gearbox as this would be the only thing doing the same speed in all gears. Cheers

Just a thought, but have you checked the condition of the upper transmission mounting?

I have and it appears fine. Cheers

Does “all the usual stuff” include the whole exhaust system from The turbo right back? If an exhaust bracket or bolt is barely touching the chassis or a component it can resonate at particular revs. Look up where the exhaust goes behind the under-engine cover, lying down behind the drivers front wheel too.

I'll have a good look around the exhaust. It's a non turbo too. Cheers

Diesel or petrol? The air intake side of the diesels can produce some odd and nasty resonances if there are holes, splits or loose parts.