Guy's I need some experienced advice (again

)
I'm really happy with this KJ, doing little jobs/mods all the time, and she's coming together really nicely now, but the whole experience is being a little tainted for me by this darn "ticking" noise (have mentioned on here before)
The engine has only covered 83k, and sounds supurb hot or cold for a diesel, no tapping, knocking, blowing etc, idle's really steady hot or cold, no clunking that you would associate with mounts etc, but when upto full working temp ONLY, there is a pretty loud "ticking" noise over the normal sound of the engine running, coming from the rear of the engine (best heard from just behind the front wheels not from front of truck) that rise's and fall's with engine revs, in or out of gear, moving or stationary, and can be heard all the time once its there

... turn off and let it cool for 20mins, and its gone again next time you start up

...
Its driving me mad, and I'm worried its gonna be something that require's an engine strip to find/put right £££££££
Its totally heat related in some way, like something expanding with temp or oil getting thinner, and to the rear of the engine around where the gearbox join's ????
I'm changing the gearbox oil this week, but not hopeful thats the culprit as the noise dosent change one bit when you engage a gear etc (manual) ... but its another job off the list
Any helpful knowledge as to what it might be in that area would be very appreciated !!
Andy.