GU Patrol driveline problem - any ideas?

Hi all,

Just returned from trying out the new camper trailer on Bribie Island - had a great time. However I noticed that my GU Patrol (4500 petrol/gas) makes a nasty thump or clunk in the driveline every so often. It's quite irregular; it happened most often in 4H on hard, fast sand - might happen every km or two. It felt to me like it could possibly be the transfer case chain jumping a tooth - is that possible? I did take a tape measure to my tyres and discovered that the fronts are 10 mm bigger in diameter than the rears (much newer, same size but different brands) so I suppose a bit of windup is possible, but I wouldn't have thought it likely on sand??? The other thing that seems weird is that it didn't do it when I got bogged and revved the guts out of it, backwards and forwards trying to get the camper out. (Ended up getting snatched by a Jackaroo, how embarrassment! :-)) Any thoughts, anyone?

Regards,
Tim Z
98 GU Patrol 4500 Petrol/Gas
04 Trackabout Safari camper trailer