Just a few days ago I started noticing this similar sound happening when I was waking my macbook pro from sleep. I thought I was going crazy until I googled this and would you look at that.... it's not just me. :/
For the record, my macbook is a 2.9/16/2tb/radeon 460.
I left the machine alone in sleep for ~2 hours before I opened it up to see if the sound would happen again. I caught it on video about 4 mins after I opened the lid, turns out I should have let the video keep going because there were 1-2 little "pops" after the one I recorded.
I've been using the computer for about 30 mins after to put together this video, no popping sounds after the initial ones...
The noise on my computer was not produced as a result of attempting to move the screen. In fact, mine never makes a noise no matter if it's been sitting 30 mins or a full day.
Anyway, here's the video:
Note: The whisping noise before the actual pop is me rubbing my nose or something.