Car Audio Pitch

Hi there, I am struggling with my vehicle's audio and I don't know how to fix it? The audio pitch plays on 1 for a second then on 2 the next second going higher and higher. I want it to go smoothly up in the pitch. Any advice I will appreciate.

Here is my car controller script:

 function Start () {
     rigidbody.centerOfMass = Vector3(0, -0.05, 0);
     
     mainCamera.camera.enabled = true;
     topCamera.camera.enabled = false;
     driverCamera.camera.enabled = false;
     reverseCamera.camera.enabled = false;
         }
     
 function Update () {
 
     speed = rigidbody.velocity.sqrMagnitude;
     steer = -1 * Input.GetAxis("Rotate Player");
     forward = Mathf.Clamp(Input.GetAxis("Move Forward"), 0, 1);
     back = -1 * Mathf.Clamp(Input.GetAxis("Move Forward"), -1, 0);
     
     
     if(speed == 0 && forward == 0 && back == 0) {
     brakeRelease = true;
     
     }
     
     if(speed == 0 && brakeRelease)  {
     if(back > 0) { reverse = true; }
     if(forward > 0) { reverse = false; }
 }
 //For Reversing
   
     if(reverse) {
     motor = 2 * back;
     brake = forward;
     ReverseLightObject.light.intensity = 0.0; 
     ReverseLightObject1.light.intensity = 0.0; 
     
     } else {
     motor = forward * -2;
     brake = back;
     ReverseLightObject.light.intensity = 1.0; 
     ReverseLightObject1.light.intensity = 1.0;
 }
 
     if (brake > 0) { 
 //Brake lights
     BackLightObject.light.intensity = 1.0; 
     BackLightObject1.light.intensity = 1.0; 
     brakeRelease = false; } 
 //Brake lights
     else {
     BackLightObject.light.intensity = 0.5; 
     BackLightObject1.light.intensity = 0.5;
     }
     
     
     frontWheel1.motorTorque = motor_max * motor;
     frontWheel2.motorTorque = motor_max * motor;
     rearWheel1.brakeTorque = brake_max * brake;
     rearWheel2.brakeTorque = brake_max * brake;
  
      FrontLeftWheel.steerAngle = Input.GetAxis("Rotate Player");
      FrontRightWheel.steerAngle = Input.GetAxis("Rotate Player");
  
      FrontSteer.steerAngle = 30 * Input.GetAxis("Rotate Player");
      
      if(Input.GetButtonDown("Camera")) {
          
          whichCamera ++;
          changeView();
      }
  
      EngineSound();}

and the audio function:

 function EngineSound() {
 
     audio.pitch = speed/10+1;

}