Whats wrong with my woofer?

I just got a brand new American Bass XFL 12D4 yesterday. Whenever I turn my radio up the sub sounds like its knocking or something. Is it because it is still very stiff? I looked in the vents and the coil seems to be still brand new and the sub is still not broke in at all. Should I just ignore the sound and still try to break it in or what? I only prolly gave it 500 watts off of my crappy lanzar amp @ 2 ohms by the way so I know I wasnt giving it too much power