Hi guys, I have a mate with a Trex 600 runing 12c  and every time he kicks it in the ass there is a strange noise and the tail plays up. any ideas what this could be. He thought originally that it was the one way bearing, then the gear for the belt drive rudder. None of those are faultly but still the problem and this is too pricey to except faulty performance.

your comments are kindly appreciated.
OrganDonor AUS