1

Why am I getting a null reference exception when I call the hear noise function?
NullReferenceException: Object reference not set to an instance of an object

this class is attached to a crate object and when it falls it calls the enemy object to come to it.

public class Crate : MonoBehaviour {

	public AudioClip collisionNoise;
	EnemyCylinder EC;
	//turns on alien hear sound.


	void OnCollisionEnter(Collision other)
	{
		AudioSource.PlayClipAtPoint(collisionNoise, transform.position);

		//BroadcastMessage("HearNoise", this.transform.position);
		EC = GetComponent<EnemyCylinder>();
		EC.HearNoise(this.transform.position);
	}
}
2

There is no EnemyCylinder script on the GameObject. You need to have a reference to an object that has the EnemyCylinder script. I would assume it is on the colliding gameobject.