Busted CV???

Hello.
I've never had a busted CV before and so I'm not quite sure what's going on?

I've got a real bad clicking noise from the front hub area of my '84 LN65 Lux. It seems to start clicking at around 40km/h.

I did a few tests. The first was to lock the hubs in but not be in 4wd. The clicking was there.
I put the ute in 4wd without the hubs locked in, there was some clicking, but nowhere near as much.

I locked the hubs in, put the ute in 4wd and drove around on right and left full lock, but didn't hear any clicking, it was very quiet.

From what I know about CV's, they always knock/rattle on full lock, but mine didn't.

The clicking seems to come easiest when driving in a straight line and when backing off the accelerator.

The clicking noise sounds similar to when a petrol motor 'pings' which sounds like your radiatior fan tapping your radiator.

I went out today with my son in the passenger seat and me driving and we both thought the sound was coming more from the middle of the vehicle rather than from either the left or right front wheel.

Any help will be greatly appreciated.
Thanks.