I just installed a 10" sub with 400w capacity and a 400w amp in my 98 eclipse and I am having trouble with static on the sub. It also constantly hits real light. I think it might be a bad ground what do you guys think?

yep sounds like really bad connections, solder everything you can.
Could also be a blown sub, they sound like static when they are blown.
also check the gains on the amp, shouldnt be all the way up .

turn the gain to about 3/4 or less, get a crossover for it if there isn't one, if you do have one, set it to low pass, make sure you black tape every connection. don't half ass it, your will will end up taking off that middle console a miiiilion times.

how much airspace is in the box vs how much it performs at


Speaks for itself!

The gain on the amp is not a bass control. It is set at the voltage of the preouts. You have 5v preouts you set the amp at 5v and leave it, bass is controlled from the deck. But as far as static goes, check grounds, yes solder all conections, tape doesn't cut it. solder, shrink wrap. A blown sub will sound like metal scraping, or grinding. You can push in the cone(ever so slightly) simulating bass and feel if the voive coil grinds, if it does its a gonner