So I just received my new MacBook Pro with Touchbar, but now I am noticing some weird periodic notification sounds without actually getting any notification. Since the sound is so fleeting, I'm not able to record it. But it does sound like two drops of water or something similar - I'm not really sure. Is there a list of notification sounds I can listen to, to maybe figure out what causes the sound? Any idea of what is might be? This is my first Mac ever, so I'm not that familiar with certain built-in alerts or application notifications. Thanks.