I believe you are correct in that you have some damping material that has come loose. Not a major problem at all. Just CAREFULLY unscrew the hex screws from the bottom woofer and slowly remove it from the cabinet. Be CAREFUL of the wires that connect the woofer to the crossover. You may need to CAREFULLY remove the wires from the woofer to clear the cabinet. Make sure you note which color coded wire goes to its repective spade lug on the woofer so that when you re-connect them they will be in phase. This should give you enough room to replace the damping material. If not, you could follow the same steps and remove the other woofer. This shouldn't void the warranty, if done correctly no one would know anyway but, you may want to check with the seller to be sure.
Hope this helps,
Mark