I got the same exact subs only in 12" (check my cardomain at the bottom of this post), in my 98. I think they hit pretty hard and have pretty decent quality. But you are getting tons of rattle out of that tailgate. Notice it only rattled once you put the gate down, which probably means something in or on the gate is rattling. The only other thing is that it is deflecting the sound back causing something to rattle. If I where you, I would buy a roll or two of dynamat (or you could use b-quite extreme. it is the same thing but much cheeper. just google it). Take the plastic off of the gate and stick it to the metal or you might be able to get away with sticking it to the plastic (i am not completely sure about sticking it directly to the plastic). This will knock some of that rattling down.