Are these digital servos? If they are buzzing is normal for them. If not, read on.

Ok, here's what you need to do to narrow down the problem.

Turn the radio on and disconnect the pushrod from the servo. If the buzzing continues then you have a bad servo. If the buzzing stop you have something wrong with the control surface/connecting rods. Something is pushing/pulling against the servo and the servo is having to push/pull back to maintain its position, and this is were the buzzing is coming from. You need to troubleshoot this and see what's causing this. Your instructor can probably go a lot further in helping you diagnose this problem than we can, simply because he can look and see the problem first hand.

Is this the Hanger 9 P-51 PTS plane you are going to learn on?

Ken