My Macbook recently has begun making a friendly "Dudoo" beep/alert noise every couple of hours at random. Sometimes it will go up to 12 hours not displaying this noise. I have looked at tons of Youtube videos and the beep in them sounds like this, http://www.youtube.com/watch?v=fOfWH8EHL74 and all commonly seems something that has to do with starting up the machine. My computer doesn't make the chirp noise either. This is not the problem I have, this will be at random when the computer has been on for some time. It's just one quick "dudoo" "beep" then nothing more for hours. At first I thought it was a program open but under further inspection the only thing open was spotify and my internet browser and it wasn't coming from them. Has anyone had this sound? What is it?