Hi everybody,
same problem here on a brand new macbook pro i7; same clicking sound, like a glass creaking. I heard the sound randomly when I touched lightly the macbook pro, i tried any part, even touching and moving the screen. The noise was there.
I followed a suggestion found on the net: just untightened all the 10 screws on the back of the macbook pro. Then I have re-tightened then, but by using a crossed pattern (first bottom left corner, then upper right corner; then bottom right corner and upper left; then center left and right; then bottom-center left and top-center right; finally bottom-center right and top-center left).
And now the awful cracking sound is gone. The problem is totally solved (for now, I hope for good).
Actually, my guess is that the sound was produced because of some mechanical stress on the bottom plate, due to a not suitable screw-tightening pattern (maybe on my unit they have used serial tightening instead of a cross pattern). Generally speaking, the wider and the thinner a metallic plate, the more critical is matching the alignment.
Full credit to the guys who figured this out first.
Hope this helps.
all my best