gearbox noise???

[graftergav]

really need some advice regards mk5 transit, went out in it today after it had been stood over the winter and heard a loud bang from underneath, but it still drove ok with no other noises for about 30 miles, parked up for a few hours then when i pulled away 2 loud bangs from underneath and then a regular thumping noise that was quite load, the noise was worse when under load / going upbank and much better when going down bank, has to drive all the way home at 25 mph. took ages. the engine seems fine and the prop looks ok to so im not sure what it is? anyone any ideas? any help would be great