Put this script in your Editor folder to be notified via your OS's default sound when Unity is about done compiling

BeepOnScriptsReloaded.cs

using UnityEditor;

public class BeepOnScriptsReloaded  {

	[UnityEditor.Callbacks.DidReloadScripts]
	private static void OnScriptsReloaded() { EditorApplication.Beep(); }
	
}