Gearbox Noise

Thanks guys for your help to my original question which I posted below, tried everything and have had it to a transmission specialist today who can't seem to fathom the noise either, he's said that he would leave it and see how it develops which is slightly worrying, he seems to think that the noise could of always been there but has now been exacurbated by the fact that I've fitted new suspension and wheels, it is odd that the noise only started after the new suspension was fitted, can anyone else maybe throw some light on this problem is there something I'm missing and is there anything else i should of done when fitting the suspension? Cheers.

ORIGINAL QUESTION:
I have a Landrover TD5 Defender, it's almost 5yrs old, I've owned it from new, regularly serviced and not worked hard, I have fitted it with Terrafirma suspension with a 2" lift plus the usual radius correction arms and rear trailing arms, poly bushes ect, it's only done 14 thousand miles, i've noticed that in 4th and 5th gear it has developed a rattle, when the engine is under load you can't hear it nor can you hear it when not under load, however if you feather the throttle gently it sounds like a bag of spanners, the noise seems to be coming from the gearbox, I've also noticed that if i build up the speed to about 50mph and dip the clutch i can hear the rattling as i freewheel down the road, i have no idea what it can be, has this ever happened to anyone before and can anyone give me some advice, thanks to all in advance.

remove front prop and try it in difflock ,there are a few bearings in gear box that can make a noise when torque is altered ,the outer races spin in case giving noise ,endfloat on layshaft can also give similar symptoms ,after trying with prop off drop some oil out of gearbox look for metal sheen