gy240 problem
 

I have a shogun v2 in which I am using a gy240. I just changed the boom to carbon and put the copter back together. The problem is that the heli will hover ok for a minute or so and then will start spinning counter clockwise. I have had it happen with avcs on and off. I watched the tail servo and it moves to the max position to the rear which is causing the rudder change. What might the problem be?