Got room for an 18" resonator?
Or yeah, like you said, another muffler....
Sounds like you might as well just go back to stock though if you're thinking of that.
Or, if you really need to keep the 3" for performance (I dunno, seems big for N/A 2.4L to me, but I'm not an expert), try laying down more sound deadening material. They make some spray on stuff that you could coat your floor with, then cover with eDead or equiv.
__________________
|