I wouldn't be too quick to send it off; I've had 3 copies of this lens and still have one, and they all basically look like that when its wide open at that distance. Its not this lens' forte, the mid to far range at wide open, where it shows lots of softening towards the edges. I would test it against a brick wall to see if the defocus is uneven, if it is even on both sides then the lens is fine.
At mid to close range wide open and at 2.8 with the subject at the center or near it the lens does very well. This is not a landscape lens. It's a low light mid to close range wide angle, where you need to get the shot. I'm not saying that it could actually be a de-centering but all the 24mm f/2 at wide open at that distance very much look like your image.

As for the CRC and rattle, all the 28f2's I have (2) and others that I've worked on have a bit of rattle due to the front CRC (as opposed to the 24 f2 and 2.8 with REAR CRC), the mechanism has a bit of play in it that does not shift the elements.