speaker popping on low notes

hey everyone i have a rockford fosgate T115 in a pro box super bass ported box powered by a JL 1000/v2 and on most of the low notes or the real punchy bass notes the speaker will pop.(anything that makes it flex alot) people say the amp is too big but i have the gain bout 1/4 of the way up and the bass boost is set on half. i have all the  bass out of the radio most times but never leaves out of the negatives and usually have the volume bout halfway. can someone tell me what the problem may be?    

How do you know it's the speaker making all the noise and not something else? Are you sure it's not an interior panel or even maybe your box is vibrating to the point of reproducing a frequency. I have this issue with my system. I'll have it turned up loud and hear a terrible rattling and with the seats folded down I can reach back and pull down hard on top of the box and it goes away.