Just upgraded the ram on my brand new 15" mbp. I noticed that after putting the cover back on, if you push towards the middle of the bottom cover it kind of pops down then up ever so slightly. Kind of like how the safety cap from a bottle of apple juice or snapple pops up and down. There's obviously a little space between the cover and the guts of the computer. It's running fine. Just wanted to see if this is anything to worry about.