So I just figured out that the vast majority of my rattling is coming from the stupid subwoofer grille. Without it, everything sounds dandy. But without it, the rear looks absolutely hideous (great cutting job back there, Nissan! Quality craftsmanship...f*cking a*ssholes). Is there anyway to somehow deaden the grille itself so that it doesn't vibrate?

 

Use small spots of Super Glue to attach it permanently.

 

Hmm...that could work. Or strips of velcro, perhaps.

 

Strips of velcro around the edges of the grille worked. But in the process of removing the grille a couple of times..I lost one of the clips. Argh. Thank God I can't hear the clip rattling anywhere back in the rear deck, otherwise I would've killed myself. Now, to sound deaden the rear trunk.