hey, i'm having some problems using the character controller, i've checked all over the web but i can't find any reason for it jittering.

this is my code:

    var controller : CharacterController = GetComponent(CharacterController);
if (controller.isGrounded) {
    // We are grounded, so recalculate
     //move direction directly from axes
    if((Input.GetAxis("Horizontal") < -0.1) || (Input.GetAxis("Horizontal") > 0.1)){
        moveDirection = Vector3(0, 0, 1 * speed);
     }
    else
     {
        moveDirection = Vector3(0, 0, 0);
     }
    moveDirection = transform.TransformDirection(moveDirection);

    if (Input.GetKey ("w")) {
        moveDirection.y = jumpSpeed;
    }

}
else
{
    // Apply gravity
    moveDirection.y -= gravity * Time.deltaTime;
}



// Move the controller
controller.Move(moveDirection * Time.deltaTime);

//KEEP IT IN LINE YOU SLAG!
transform.position.x = depth;

and it's all housed in a 'FixedUpdate()' function

any ideas? thanks in advance