Intermittent ding/sonar sound coming from Macbook Pro... even when turned off! My MacBook Pro late 2014 is making a ping sonar-like noise every 30-35 seconds, even when muted and the laptop is turned off. It seems to be coming from the left side of the MacBook and is very loud.
I've made a video so you can hear the sound and how frequently it occurs (first noise at 0:14, then 0:53 and finally 1:31).
There is an alert noise when logic board is failing/has failed. 

Have you tried various start-up options?