The first time I heard it I thought my axle was about to break or something. Every now and then I am driving and I hear this not loud but definitely noticeable clicking noise that is caused by large rocks/pebbles getting stuck in the Terra Grapplers. I just pull over and get the rock out when it really annoys me. Does this happen to anyone else? In all the threads I searched before buying the tires no one ever mentioned this. Don't get me wrong though, I still love the tires.