Funny noise in 4wd

Hi
I have a 2000 gu dx 4.2td ute ive only recently got the car. It drives fine in 2wd i took it to the beach about 3 weeks ago and when driving through the very soft sand sounds like from the rear you will hear a sorta bang sounds similar to a rock being smashed i think when this happnes the whole rear of the car gets unseattled and it surges forward. But being in the soft sand under the tide line i want going to stop to check. i went again last weekend forgot about the noise went for about 2 hours in low range up some tracks was fine then came back though soft sand did it again like last time. ive now had sunrasias fitted and they have for a more woren tyre on one side at the back then the other i tried 4wd on gravel and it makes the noise a fair bit but only surges the car forwards.
Can any one help me im getting worried it might fail on me when i need it to get me out of trouble.
Thank you

Sounds like one for Paul, Tony and crew - hang tight mate, someone will be able to offer some suggestions.

Hopefully someone can help you out mate. If it's happening in low would it be possible to have someone walk behind you try and identify the clunking area maybe?

Never had a patrol tranfer case apart but if they use a morse chain in there (and I think they do) it can exhibit that sort of symptom if it is stretched and jumps a tooth, I have seen this in ford/mazda utes and ford explorers that have done a bit od 4WD on hard surfaces or with missmatched tyres. happens worse on turns when driveline winds up

Thanks that fits into what im hearing but still very open into others opinions Also it does it in high and low range.

phil you have written worn tyre on one side than the other. how much of a difference is it ?

well i should add that it started when they where all pretty similar i then had the wheels changed and one back is like 30 % other back maybe 60% and it's got worse don't know if the problems getting worse of the wheels have changed things it's also got a different brand on the front and their abour 70 - 80%

checked your tailshafts - uni joints and slip joints . how many km's on it ? service history with oil changes ? and a ute - spring leaf or coil ?

its done 290000 i checked unis recently and good look underneath all looked good it dosent have log books but been serviced all the time its leaf rear coil front

i may have the reason for the sound for you bud. A while back i drove my "old" GQ up to double island for the day, that afternoon we went home through high tide and the first bit of soft sand i hit in H 4wd the truck had this wierd winding up sensation and the followed by a bang that scared the crap outa me. Pulled over and had a look around to find that one of the kids had been screwing with my fron left hub and it was half engaged. I locked the hub up and went for a bit more until the next bit of soft sand and then bang again with that wierd winding up kinda sensation again. Pulled over and she was half out again.

I too thought it was from the rear but ended up being my hub. Strange thing is i got home pulled it appart and no damage was to be found! i cleaned everything back up, re greased and threw it back together only to never have it happen again. Might be worth a look as it sounds exactly like what you have mentioned.

It also didnt do it in Lw4d only in high for some reason.