Right if it is a uj gone on the front prop - piece of piddle not a problem easy job to fix, also cos of manual hubs and 2-4 selection on gearbox the front prop only moves when you lock everything in for 4wd, its an easy job for a garage to do takes me ten minutes in my workshop with a vice, the other noise it could be is a cv joint, but then again will only clonk when whole lot is needed in four wheel drive, the cv joint is more awkward as to replace is a bit costly for a new shaft, the hub has to all come off, to someone like myself its easy but is also time consuming in garage terms, so labour will be a couple of hours, but having said this most cv's clonk on old fourtraks anyway but still keep going for years, just make sure there is plenty of lithium grease in the hub - the filler is behind the wheel and disc brake, its a 24mm nut on the top, if clean you will see it easy, its not really a major issue if you have a secondhand one kicking about aswell, its just a case of getting it replaced. What you want to do is test it to see if it is a cv, put it in 4wd low full lock on the steering and drive if it clicks - cv going, if it clicks when wheels straightened - cv bad, if quiet then i would not worry a might unless you are about to do a ton of heavy off roading, if no noise at all but a 'tink!' then this is a simple uj on the front prop, you can test the uj's by getting underneath, put whole lot in 4wd, then with a pair of gloves try to turn the shafts vigerously left and right to see if there is movement, if there is then its the uj's going - it will be visible and obvious, hope this makes sense i rabbit on a bit sorry, any other probs just ask.