It sounds although your cv one or both are on their way out fill with grease ASAP and they will last a while. Only in diff lock because your trans windup is putting more stress than usual through the transmission. A lot of strain goes through when you
A have grip,
B have the centre diff locked,
Although not advised if the motor is in gwo a short session in centre diff lock on Tarmac should be ok. More often that not on tight slow low range corners you get skipping wheel slip inside rear spins and loses grip making a noise but its not a clicking noise.