honestly, its probably caused from the mass transit of mbps in the factory. its made from a solid block of aluminum, chopped, drilled, etc. My mbp has some minor flaws like a faint line that runs between the : button and the " button...when i slide my finger over it, it doesn't have an indentation. its like a smooth line (hard to explain, but im pretty sure their shouldn't be any line there). plus on the lid of my mbp, theirs a visible indentation that i can see at a certain angle in the light, when i slide my finger over it, that too also feels smooth and solid. soooo yeah...hope that rant helped lmao.