Ok! i've had the diff go! big style! resulting in clonking noise left right and centre still got the remains of my diff if anyone really wants to see!
know what happens is the plante gears in the diff housing wear! this is due to bigger wheels and hard acceleration in the low end gears! resulting in teeth slowly wearing leaving metal folting around the box!
easist way to find out if its the diff is jack one side of the car up better on the NS but it in gear and rotate the wheel see if you can feel any play! then repeat with it in 1st and 2nd gear! if excessive play the plante gears could be on there way out
Or you could just drop your gear box oil and any bits in it that shouldn't be there then panic
its your call then if you strip the box apart or not!
but let me know cause if you do it yourself its a bitch to break the box due to the reverse bar and pin!
Hope you get it sorted