I feel like it is just related to the modchip's extra space it is consuming pushing just a little bit on the metal shield. If I take the back cover off, the crack disappears until it is reinstalled, but nothing looks out of place underneath. I was just curious if others have this issue or if I should be worried about longevity of it.The back cover is very thin so it can be either due to impact from the outside or something sticking out more that it is supposed to.
If it is due to internal pressure on the casing, you might want to check it out else that crack might go all the way to the edges.
Are you sure it is not the metal casing or the screw in that area sticking out just a millimeter too much?