Object clashing with terrain.

Physics
1

I have a game object that I can move around with a simple script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Player : MonoBehaviour {

    private float moveSpeed;
    private Vector3 playerPosition;
    private Rigidbody rb;

    // Use this for initialization
    void Start () {
        rb = GetComponent<Rigidbody>();
    }
   
    // Update is called once per frame
    void Update () {
        if (Input.GetKey(KeyCode.LeftShift) && Input.GetKey(KeyCode.W))
        {
            moveSpeed = 22;
        } else
        {
            moveSpeed = 10;
        }

        player_movement();
    }

    private void player_movement()
    {
        if (Input.GetKey(KeyCode.W))
        {
            rb.MovePosition(Vector3.forward * moveSpeed * Time.deltaTime);
        }
        if (Input.GetKey(KeyCode.S))
        {
            rb.MovePosition(Vector3.back * moveSpeed * Time.deltaTime);
        }
        if (Input.GetKey(KeyCode.A))
        {
            rb.MovePosition(Vector3.left * moveSpeed * Time.deltaTime);
        }
        if (Input.GetKey(KeyCode.D))
        {
            rb.MovePosition(Vector3.right * moveSpeed * Time.deltaTime);
        }
    }
}

However, the object keeps clashing with the flat piece of terrain I have set up and I don’t know why it is doing this. I have a small video of what it looks like when it happens here https://vid.me/dp9d. What is actually happening here?

2

i notice there are 3 terrains in the scene. Are any interpenetrating? you can get violent vibrations if 2 colliders are placed inside each other.