Please consider an option to toggle the success/fail sounds, or just remove it altogether. I feel that while they can be informative in the sense that you know immediately if you failed a level or succeeded, that the sounds are very annoying and distracting.
For example, when I play a level, but then I figured I play the wrong level and want to change it, then I hit the exit level hotkey, I get the fail sound.
When I test my single level and see a minor mistake I want to fix, I hit the exit level hotkey...fail sound.
If I don't want to hear the success/fail sounds, the only thing I can do is mute the sound, which in turn will mute any lemming activity when playing the game.
Seeing text in front of me that tells me if I beat or failed a level is more than enough. So please either add the toggle option, or just remove it completely.