Sounds like the amp you tried was clipping and damaged the suspension then. Or you had a bit of a combination of clipping and leaking and damaged the suspension. Does the popping almost sound metallic?

yes, almost like a rattle

Take them out of the box and listen to them free air and see if the sound remains. If so its possible that like Toofatt said, youve damaged the suspension somwhow.

the rattling sound was not present when i took the subs out of the box. does that mean its definitely a box leak?

Yeah its definitely something to do with the box and Im almost certain its not the sub. If it was a problem with the suspension it would be bottoming out easier when outside the box.

So I do think it is a problem with the box but I doubt its a leak. A leak would generally just act like an improperly tuned port and at worse youd get some port noise but I kinda doubt it. My guess actually would be the box itself is rattling somehow maybe by improper construction or something. My specialty is in tuning and speakers so Im not that well versed in box design and such but I would check the box to make sure it was put together properly and nothing is coming loose anywhere. Better yet, slap together another box and see if that one has the same problem.

What kind of box is it? Is is a dual sealed? If so the center panel in a cheaper constructed box likes to come loose and resonate. If you didn't build the box yourself, I would just trash it and build your own. These prefab boxes use staples and cheap adhesives. If they used the adhesive I used you can get away with staples, but I used screws as well. If you a table saw then building a box will be simple and come outer perfectly. You can use any saw really, but a table saw would make perfect cuts. I can set you up with a few good links on building tips if your interested.

Just trying to fix this box is only a temporary fix. Assuming its the panel in the center, your not going to really be able to get any adhesive in and around the edges enough so it will glue strongly. And the screws you put in will only hold for so long. Vibrations and screws in wood do not mix well. Building a box is simple, and even easier if you have a friend or someone to help.

yea its dual sealed pre-fab. the divider board doesnt budge at all. but i guess even the smallest movement will cause big noise

how much does the mdf and carpeting usually cost? i just got a ticket so now im on a tight budget until i know how much the ticket will cost me

Well under $50 you can get everything with material to spare with mistakes. Bang on all the panels, they should be sturdy as can be. Don't just knock on them give them a good bang. You can tell from the sound of hitting it.

2 weeks ago, it cost me $45 to build my 3/4" dual 12 MDF box without the carpet and I'm 8 screws shy. I used a sheet of 3/4" MDF, a 100 box of #8x1.25" screws and 2 tubes of liquid nails max strength.