Whenever my subs cone has alot of excursion, I'm getting a slap or a tapping sound from the cone. It is a Powerbass L-104D in a sealed enclosure with an Alpine MRX-M50 amp running it. Also using a AudioControl LC2i LOC. Gain is half way up (nom), LP is set a hair below 80 Hz, subsonic at 25 Hz. Sometimes I find myself wanting more, so I try to turn the sub up more using the remote gain control knob. Anytime there is a kick drum or something sharp like that, the cone taps. Annoying. Definitely happening during big excursions. May be time to try another sub in that box. Its a custom sealed fiberglass enclosure under the back seat in my dodge ram quad cab. Approx .70 cu ft.