Why is my parallax script stuttering?

I have a background element (a distant island) that I am applying this script to. It is supposed to have a very small parallax effect, so I used a value of .98, where 1 = no parallax effect. However, while the parallax effect essentially works, it jitters a pixel or two quickly left/right and up/down at random intervals.

The Cinemachine camera is set to follow the player.

public class Parallax : MonoBehaviour
    private float startpos;
    private float startposy;
    public GameObject cam;
    public float parallaxEffectX;
    public float parallaxEffectY;

    void Start()
        startpos = transform.position.x;
        startposy = transform.position.y;

    void Update()
            float dist = (Camera.main.transform.position.x * parallaxEffectX);
            float disty = (Camera.main.transform.position.y * parallaxEffectY);
            transform.position = new Vector3(startpos + dist, startposy + disty, transform.position.z);