MacBook Pro :: Removing Underside Of MBP 17 - Pop Sound When Removing On Cover Normal?

as an extension to my question regarding RAM utilization, I've decided to upgrade my RAM. I went through the process of removing the underside of my MBP. After taking the screws out and mentally marking which slot they came out of (some are of different size), I pulled the lid up at the black trim area (the "neck" of the display mount) as this was the easiest way to get a non-damaging grip on the metal underside -- read: I avoided using a screw driver on the lid. As I started to lift, I was surprised at the amount of force I needed to use in order to remove the lid; something near the center of the cover was still holding the lid to the underside of the body. In fact, the amount of force I needed to use made me pause to question if I missed an important step other than simply removing the screws. I decided to "go for it" and applied more pressure while pulling the lid up and away from the body and heard a "pop" noise.