You mean... it wasn't there when you bought it?? Hmm. That's kinda suspect.
I once bought a MAC e/s with a nick in it. And I knew it had been opened because you know the box, it has two small flaps, one on either side? and one of them was bent back in, when they are always facing outwards with a new product, but if someone was jamming the e/s back into the box in a hurry, they might not notice and fold the little flap in, instead of out.
I was pretty peeved but for my particular case, I didn't feel like bringing it back.
Still, I hate when you pay good money and get something not up to par.
You should def. return yours.