Popping Noise

If you have a grille on the sub's box, make sure the sub's cone and/or surround is not hitting against the grille when the bass hits.  An easy way to check obviously is to remove the grille and see if the problem continues.  Let us know what you find out.

Just FYI this type of problem is more likely to happen with a sub like yours that has a large amount of excursion (linear cone movement).  The deciding factor though is usually the type of grille that's used, and how it is mounted to the sub's box.

No it doesn't have a grille.

ucantbeme......ive seen your problem happen before with many different reasons. since you dont have a grill in place, how high is the gain turned up on the amp? try turning the gain back say a quarter of a turn and see if that cures the problem. if not, look to see the condition of your rca cables. one of the number one cases of popping or crackling of a subwoofer is overdriving it or the amp. even though your sub maybe rated for 1400 watts, if its not in the correct airspace for it to drive properly, you can over drive it. and it wont happen over night. but after time of driving the sub really hard or beyond its limit, the popping can accure and eventually it can result in failure of the sub altogether. hope that this helps.