It sounds like you either need to lube the tail section somehow (not sure as I don't have the bird either), or you need to decrase the pitch if the main rotor spins clockwise, and increase it if it spins counter clockwise. There should be some servo links that you can adjust. Again because I don't have this heli, I dunno if you would need to lengthen it or shorten it. I would also check that the pitch assembly on the rear rotor doesn't bind and moves quite freely.

If you can, it would be a good idea to get someone who has flown heli's before to take a look at it. I know that it is not always available, but if you can that's what I would do.