In forward flight, the faster you go the more it will bank right. It's the nature of a single blad Heli. I can explaiwhy if you like but it's described more than one place in here.
Now did you trim out the servo rod ends before triming electrically? I have found this really effects flight responses when flying in low rate mode.
They tail motor will buzz oddly all the time. That's the gyro adjusting it's rpm to maintain correct heading. Hold in your hand with blades turning and rotate it left and right. You will here it trying to keep fight against your movements.