Xsite Subwoofer Making Noise

I have two xsite sub woofer with a 1500audiofonics ok . My car had a problem and i haved to fix it well then i removed the sub and put it in my closet. When i fix the car i put my sub"s back and one of the subs when it hits hard it sounds like something hiting it in the middle its a doble coil speaker and the other one sounds good. But the thing is when I removed it they sound good but now one makes that sound what could it be?

Please be more specific with your equipment....might as well told use you have some subs and an amp...not much that we can go by to figure out whats wrong How are your subs wired?? What amp is it?? model?? specs?? What are the specs on those subs??

My amp is aaudiofonics 1500 is 200-2ch at 4@ and 300 at 2@. My sub'sare two xsite or xzite dualcoils the violet ones there are 400 watts. I have a clarion dxz555mp, I have a pre amp with 7 bands and sub output.All the cableis good because i put the good sub in the same channel its sounds good and then i put the bad sub in the same channel and it sound good but it makes a noise in the middle of the sound like something hitting it. What could the sub have?

something loose inside the box?

nop I open the box and everything is good the sound comes from the center of the sub

sounds like the wiring is wrong and the sub is bottoming out. What enclosure is it in???

But i have the same subwoofers and there connected the same.The thing is when i put the damaged sub high it makes like a poping noise or like something hitting it in the middle of the sub.

you are making no sense...how are the subs wired to the amp?? how are the subs coils wired??? simple questions...just answer it

Can anybody tell me how to fix a xsite subwoofer?

free air the sub and listen and watch. must take the sub from the enclosure to see if there is a problem . sound to me like a loose dust cap and u will find out when freeairing.  cover the rear pole vent and it will flap if loose. just use some super glue to fix...