It's hard to tell if you have a problem without looking at it, but digital servos do chatter a bit from slight (normal) stiffness in the linkages. They continuously try to hold a position and so a little bit of chatter/whining is to be expected. Servo chatter could also be caused by abnormal stiffness in the linkages (binding), a damaged receiver crystal, interference, etc. Expect it on the rudder servo any time the heli is in hand....the gyro is very sensitive to movement.

Realflight includes tutorials. Slow forward flight emphasizes tail control and faster flight demands more cyclic control. Practice, practice, practice, mainly on what you intend to do with the real model. It's important to get very comfortable with all directions of hover. Every new thing you learn well will reinforce all the previously learned skills.

Good luck.