For warrantly situations, I'm not sure you would have to pay anything, that is if you don't like your speakers within the 30 day window.
My first 500 had a rattle. I know this is a stupid question, but how do you have the volume(gain) setup on the sub and receiver. If your running it to hot with no calibration you could be working the driver to much.
With my rattle I worked with Axiom via phone and email to try to isolate the rattle:
First I checked to make sure it was actualy the sub and not something in the room nearby. Heck, when I first ran my test tones off the Realtraps test cd I heard all types of rattles in the room.
Second, Axiom had me check all the screws for the plastic port below the driver, and the driver to make sure they were snug. Air escaping can make funny noises. I even removed the driver (it is very heavy, unhooked the wires) and checked the screws/fasteners on the inside to make sure they were snug.
Third, sometimes the wiring on the inside of the cabinet bounces around on top of the port making a vibration noise, I checked that as well as it appeared I had a lot of slack in my wiring.
Then I moved around to the back of the sub, and could hear the noise louder near the back amp plate. When I applied pressure to the plate in different locations the noise either got louder or softer. So, they had me remove the amp from the back by taking out the bolts around the perimeter. (again this bad boy is very heavy)
Fourth, ok once the amp was out I noticed the rattling seemed to be coming from within the amp, I noticed one of the + positive wiring terminal seemed loose. I tried to tighten it the best I could, and also took some electrical tape to hold it in place so it would not jiggle. I still had the noise.
So I and Axiom determined that there was something on the inside of the amp that was making the noise. The amp is virtual impossible to take apart unless you know what your doing, so they sent me a replacement.
All was good except the first replacement was destroyed by Fed-Ex. I had a long thread about a year ago showing the damage. Looked like the dang crate well off the truck and got run over by the truck.
They sent me another one and all was fine.
Long story short, just call Axiom and they will help you.