What is this caused by?
 

Been having some weird knocking noises and vibration in the rear end. I jacked the car up and saw that the passenger side shock looked like it wasn't totally straight and it was rubbing against the sleeve. The other side of the car is fine and everything looked to be installed correctly when I was taking it off. Could this be the culprit of the weird noises and how can I avoid this happening?

http://i54.tinypic.com/23vgk6v.jpg

bent shock?

maybe u hit the curb alittle to hard when parking or a really bad pot hole i think would do that. If u are going to replace make sure u do both front shocks.

That doesn't look like a stock shock to me. You need to stick with the way the Mazda engineers designed it.

Or get some upgrades if what you got doesn't still work (rare situation). Check out respeed for this stuff.

My exhaust hit my shock in that same spot on my first FB. It rattled like crazy on rough roads.

Could be just the shroud that's bent, but it needs to go.