I took my rear deck out and put my 6x9s in the deck so it not touching the metal it work well so far

 

What?^

Yes, some rear fill can be useful. But most of the time it isn't needed. Which is what I learned from these guys, and from reading up on it. When you go to a live concert, do the musicians play behind you?

I also had the rattling problem with the rear decklid though. Instead of covering the whole thing with sound deadener, which I may do eventually, I just had some foam laying around (I think it was for a bike helmet or something) and hit the decklid with my hand to find out where the rattles were coming from. You can usually see where there is a gap between the decklid and the metal tray and that is usually where it vibrates. I just wedged in a few pieces all the way around the decklid where there were gaps and that took care of the problem.