if u put the amps dedicated to eache sub it wouldnt make it louder or deeper but more clear. There wouldnt be much distortion. But before u do that make sure that you know the maximum amount of watts ur subs can run because those amps are probably 300 X 2 channel meaning ur giving each sub 300 watts right now but if u just hooked one up you could be giving it 600...Im pretty sure ur subs can handle 600 though. O and ur not the only one with a rattling back end. I had a little crack in my center taillight section and my subs make it crack from 1 in. to about 5 :). My license plate rattles also.