Its a known issue. I've been through countless replacements and they all have the same issue. Seidio doesn't really care so if its gonna be a problem for you I highly recommend returning it before its too late.
Mine has done this from day 1, the fit just isn't perfect, I heard a lot of people talking about the top part, but it was the bottom that was the problem for me.
Now I've fiddled with it a little bit trying to get the fit right and it broke one of the tiny little clips off, but I'm not going to buy another one anytime soon, those are too expensive to just buy another one.
I noticed mine creaks a little when I squeeze it, especially towards the bottom right, but it never does that in everyday use. I did drop the phone a few times, though, so perhaps it bent the case a little bit.