Free-look camera y-rotation shake

It's the mouselook with inf and -inf plugged into the limits. There's no code to see other than the default behaviour when the range of motion is changed in Unity.

 [AddComponentMenu("Camera-Control/Mouse Look")]
 public class MouseLook : MonoBehaviour {
 
     public enum RotationAxes { MouseXAndY = 0, MouseX = 1, MouseY = 2 }
     public RotationAxes axes = RotationAxes.MouseXAndY;
     public float sensitivityX = 15F;
     public float sensitivityY = 15F;
 
     public float minimumX = -360F;
     public float maximumX = 360F;
 
     public float minimumY = -60F;
     public float maximumY = 60F;
 
     float rotationY = 0F;
 
     void Update ()
     {
         if (axes == RotationAxes.MouseXAndY)
         {
             float rotationX = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * sensitivityX;
             
             rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
             rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
             
             transform.localEulerAngles = new Vector3(-rotationY, rotationX, 0);
         }
         else if (axes == RotationAxes.MouseX)
         {
             transform.Rotate(0, Input.GetAxis("Mouse X") * sensitivityX, 0);
         }
         else
         {
             rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
             rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
             
             transform.localEulerAngles = new Vector3(-rotationY, transform.localEulerAngles.y, 0);
         }
     }
     
     void Start ()
     {
         // Make the rigid body not change rotation
         if (rigidbody)
             rigidbody.freezeRotation = true;
     }
 }

Here stills shaking!