A Unity script to play a sound effect when script compiling starts and ends.

CompileIndicator.cs

using System;
using System.Reflection;
using UnityEditor;
using UnityEngine;

// I recommend dropping this script in an Editor folder.
// You should have two audio clips somewhere in the project.
// You'll need to edit-in the paths of those clips (from your project root folder) in the static initializer below.
// Example path: "Assets/Editor/CompileIndicator/start.mp3"

namespace Assets.Editor {

	/// <summary>
	/// Plays a sound effect when script compiling starts and ends. 
	/// </summary>
	[InitializeOnLoad]
	public static class CompileIndicator {

		private const string CompileStatePrefsKey = "CompileIndicator.WasCompiling";
		private static readonly AudioClip StartClip;
		private static readonly AudioClip EndClip;

		static CompileIndicator() {
			EditorApplication.update += OnUpdate;
			StartClip = AssetDatabase.LoadAssetAtPath<AudioClip>("REPLACE_WITH_PATH_TO_YOUR_START_CLIP");
			EndClip = AssetDatabase.LoadAssetAtPath<AudioClip>("REPLACE_WITH_PATH_TO_YOUR_END_CLIP");
		}

		private static void OnUpdate() {
			var wasCompiling = EditorPrefs.GetBool(CompileStatePrefsKey);
			var isCompiling = EditorApplication.isCompiling;

			// Return early if compile status hasn't changed.
			if (wasCompiling == isCompiling)
				return;

			if (isCompiling)
				OnStartCompiling();
			else
				OnEndCompiling();

			EditorPrefs.SetBool(CompileStatePrefsKey, isCompiling);
		}

		private static void OnStartCompiling() {
			PlayClip(StartClip);
		}

		private static void OnEndCompiling() {
			PlayClip(EndClip);
		}

		private static void PlayClip(AudioClip clip) {
			Assembly unityEditorAssembly = typeof(AudioImporter).Assembly;
			Type audioUtilClass = unityEditorAssembly.GetType("UnityEditor.AudioUtil");
			MethodInfo method = audioUtilClass.GetMethod(
				"PlayClip",
				BindingFlags.Static | BindingFlags.Public,
				null,
				new []{typeof(AudioClip)},
				null
			);
			method.Invoke(null, new object[]{clip});
		}
	}
}

If anyone comes here in 2022 the reflected method is now named "PlayPreviewClip".

Use the following in Unity 2021

private static void PlayClip(AudioClip clip, int startSample = 0, bool loop = false)
{
	var unityEditorAssembly = typeof(AudioImporter).Assembly;
	var audioUtilClass = unityEditorAssembly.GetType("UnityEditor.AudioUtil");
	var method = audioUtilClass.GetMethod("PlayPreviewClip",
					       BindingFlags.Static | BindingFlags.Public,
					       null,
					       new[]
					     {
						typeof(AudioClip), typeof(int),
						typeof(bool)
					     },
						null);

         method.Invoke(null, new object[] { clip, startSample, loop });
}