I had it happen when I used to use taper nocks on aluminum shafts and just twist them on for target shooting but I've never had it happen with a collet type nock system (uni-nocks). If you hear arrows impact each other you need to check the nocks and the carbon shafts for damage. Oh, when I've had it happen there wasn't any damage, but that was a wheel bow at 55#'s, not a lot of energy there.