What kind of headunit are you running? The interference you're getting could be coming from the deck. the reason you're not getting it through the sub is that the sub's amp has a x-over that cuts off the frequency range of the intereference. I'd pull the headunit and find a better ground location for it. If need be, drill out and tap a new ground to bare (not painted) metal. I'd also find a better grounding point for your amps/cap. Make sure the ground location is not father that 2 feet from the farthest component.


I'm still not clear as to the type of "static" you're having. Is it more of a "whine" than static? If it for sure static like from a tv and it doesnt change pitch ever, it could indicate a faulty connection, most likely your RCA signal.

Try using a different RCA cable (no need to run it through the car - Just for test purposes). All in all I believe it's going to be a ground loop issue and can be remedied by finding better grounds for the headunit, the amps/cap and even underhood for the block/alternator/battery to chassis.
I believe in the integra, there you can just sand down some of the sheet metal under by the rear strut towers and tap a large bolt to it. Perfect ground.