clicking hubs when not in 4 wheel is due to the inner assembly running a bit dry on lube, and starting to drive the shaft, but as it is not the shaft driving the hub it leads to this clicking if it gets realy bad it can make the wheel jump, you need remove the large multi turn circlip and pop it out, if has started to pick up just rub off with fine wet and dry paper, oh and watch out for the super thin ball washer in the bottom, wipe some grease round it and put it back together, make sure you do both sides, Rick