Plane engine sound change when press key? (c#)


I am trying to make a game, where there is a plane, and the engine is Emitting a sound from a sound source, when i press W + Shift the plane accelerates. I want to use another sound for the engine when i press W + Shift and when i let go, it goes back to the regular sound. but so far i couldn’t do it. Help?

using UnityEngine;
using System.Collections;


public class Example : MonoBehaviour
	public AudioClip sound1;
	public AudioClip sound2;
	void Update()
		if(Input.GetKey (KeyCode.W) && Input.GetKey (KeyCode.LeftShift))
			audio.clip = sound1;
			audio.clip = sound2;
			audio.Play ();