http://www.kicker.com/sites/default/files/2010%20ZX%20350.4%20650.4%20RevG.pdf

 

Unfortunately, it doesn't look like that amp has a whole lot to offer a sub... it's more designed for highs.

 

Yeah I can only control how high the freq can go on the sub. So right now I have it set to about 100hz max. Speakers take it from there.

 

If you only hear it when you open the hatch it's a loading issue, and it's bad. edit: it's bad if it's noticeably sounding bad, or if it's over-excurting. With no SSF, keep an eye on it.

 

No I said I can only hear the flapping when oppening the hatch, the bass is super loud and awesome.

 

That's what I meant. If you hear flapping while the hatch is open, it's because the cabin isn't putting as much pressure on the sub, allowing more cone travel.

 

I can still hear it if I go in the back seat and look over, I just mean its not super noticeable.

 

flapping isn't good...it means something is mechanically smacking something else. Get an outboard crossover like a kicker kx3 or similar with a subsonic (infrasonic) filter, or an fmod passive in line rca bass blocker(not as good as the first suggestion).