It is unclear as to why these sounds are occurring, and what might be setting it off as there does not appear to be any rhythm to these sounds and that they happen at random intervals. However it is noticed that they do occur when intensive tasks are happening, which has led to speculation that the sound might be coming from the hinges where the heat from the laptop is causing the glue or some plastic component to start to lose some of its integrity.
This seems to be more prevalent in the 15-inch MacBook Pro which has a heavier display. One customer writes, “I think the problem is actually from the hinges, as there is some natural flexing in the aluminum back of the display. I think the heat has affected the glue or some plastic mount in the display assembly.”
Another customer has since backed those claims up by saying, “I am able to constantly reproduce the sound by pressing right at the bottom of the screen assembly in the middle.” Now we can’t say for sure what the issue might be, but perhaps you’ll want to keep an eye out for it in the future.