first off, i have no experience with the gear boxes. when I'm just rolling the wheels my rear gear box has a catch in the same place every time. Iv had the problem before, and now its back. how i fixed it last time and this time it just take it apart, and i saw nothing(no broken or bent teeth in the drive gear or the diff gear, so i just put the case back together and it works fine. i just want to no why it happens and whats causing it??