Help identifying alarming noise

Hi I am new to the world of Jimnys.
We have just purchased a Jimny which is generally fine, except for an alarming noise which occurs occasionally from the underside of the car (under gear stick area).
It occurs during general road driving when slowing gently using gears in 3rd & 4th . The noise is like gears grating but not quite meshing (does feel like car goes into neutral- but cant say that for sure). Noise lasts 1-5 seconds & ends with a load mechnical twang, after which all is fine.
May be coincedence but pressing clutch can stop noise when occuring.
Have looked under car & nothing appears amiss,( transfer box secure, normal play in propshafts)
Any ideas what could be the matter would be much appreciated?

Thats a hard one.

It almost sounds like the transfer box chain is slipping but I have seen that happen in first and second gear, not 3rd and 4th.

The other thing could be a failing UJ, but the bit about it going when you dip the clutch is strange.

My suspicion is that there is something not happy in the gearbox, particularly if it has the feel that it is in neutral (can you rev the engine freely when its happening, ie. this would show the engine is not connected to the road wheels)

Thanks for help.
I shall do some more tests. Trouble is it happens just when your not expecting it & is difficult to make happen.
The clutch point may be a red herring, but will check if quick enough next time it happens.
If i was asked to describe the noise(with my limited Jimny knowledge) i would say its like the car is jumping out of gear, then something twangs (sounds like a metalic rod) that rights it?

Is it stick in 4wd? Jack up one side and see if a front and rest wheel spin when you your in 2wd.

Check the mounts on the transfer box and also the mount at the end of the gearbox

pretty sure not stuck in 4wd, but will do test.
Was underneath car last night, didnt check gearbox mounts but it was possible to move transfer slightly- seemed acceptable .
Will check gearbox mounts.
Many thanks

Does it actually jump out of gear or just sound like it does?

Double check everything for rattles. Mine made a god awful noise that turned out just to be heat shields on the exhaust. There are loads of them including one on top of the backbox (assuming its an original backbox) which is hard to see when its on the car. From your description it sound a bit unlikely it will be that but always worth checking the easy things first!