Servo Question

I have assembled my JD Humanoid Robot. When I connect to him, one of the servos makes a buzzing sound and won't stop unless I turn it off. For instance, the servo was the upper part of the left leg. When I connect, it lifts the left leg all the way and buzzes. I then switched the servo to an arm, and when I connect, the servo bends the arm fully and buzzes. I am not sure what I need to do to fix the problem.