Cruiser making weird sound in 4wd

Back again with another ask! Been on our trip and everything went well with the water tank up within the canopy frame which was a huge relief! Thanks for all your input there (as well with the fridge - we ended up just hiring a chescold for the trip to try before we buy and quite impressed by it!)

Situation with the cruiser though (75 series) when we put it in 4wd...going through sand -mainly on the soft sand but occasionally on compact sand as well we heard a very bad 'clunk/bang' sound and vibration coming from the passenger side rear tyre. We seem to think it maybe the rear axle or diff but unsure.

Also (when not in 4wd) , when we go to use full steering lock on road and also when it is heavy load on back going around corners or round abouts we hear the 'clunk/bang' sound in the front suspension, and I can also feel a bad vibration in the steering wheel .

Does any one have any ideas why it is making this sound because we really want to go 4wdriving in future (which we couldn't this time around because of the problem.....in actual fact, the 'clunk/bang' sound felt and sounded similar like we had a flat tyre. (we had the tyres on 20psi)

My boyfriend loves his cruiser (i do too) so we really would love it if you had any suggestions about this before we take it in shop

Thanks guys!