SoundPop(excerpt only).cs

    void FixedUpdate () {
        // non-pertinent code not depicted
        
        if (thrust > 1.0f) {            
            PlayThrustSound();            
        } else StopPlayThrustSound();        
    }

    private void PlayThrustSound() {
        if (!ThrustSound.isPlaying) {
            _thrustVolume = 1.0f;
            ThrustSound.volume = _thrustVolume;
            ThrustSound.Play();
        }           
    }

    private void StopPlayThrustSound() {
        //float _StartTime = Time.time; 
        _thrustVolume -= 0.03f;
        ThrustSound.volume = _thrustVolume;
        if (_thrustVolume <= 0.0f) {
            ThrustSound.Stop();            
        }        
    }