This problem usally happens when you have too much tail whip, what type of rest are you shooting through? I am also shooting the same arrows with plastic fletching only I am shooting with 100gr. 4 blade Muzzy's and a shoot through rest. I had encountered the problem you are now adn fixed the problem when i went to a shoot through rest. If you are shooting through a shoot through rest try moving your rest pins closer together or moving your rest outwads a little bit so the arrow doesnt touch the bow, I think youll find these tips may cure your problem.