Mrashtray
I also have the Shogun 2. I am also working on getting out a vibration, But it's a small vibration and also at this time appears to be in the tail. Anyway something you may want to try. I read a post sometime back where a guy had a similiar problem as yours.
The guy said that he finally got it solved by moving the tail boom supports. I cant remember if he lenghted or made them shorter, but he claimed it got rid of the problem, (Resisdence Vibration).