f-ing annoying, fix one then another pops up.
sounddeadner and closed cell foam will firm everything up. use a "mass loaded vinyl" barrier if you want to actually get rid of wind and road noise. you only need to use as much sounddeadener (foil and compound) as it takes to stop the rattle. 1/4 of the steel panel is enough to provide 90% of damping effect that is possible. thick closed or open cell foam is then used as a decoupler to separate the plastic panels from the steel. mlv barrier will block remaining sounds.
a lot of times rattles can be quieted by lowering the bass boost.
Its one of the biggest culprits of the rattle, and in a tuned system you really shouldn't need use it. cabin gain already supplies all the boost you would ever need. keep the gains higher and bassboost lower and you will be less likely to rattle so much. sure that one note at 50hz is fun to see stuff shaking and feels cool, but the rest of the notes need juice too. you pull juice from the other frequencies to supply that boost.
with 3 12's you shouldn't need it on at all. with that many subs you must have one hell of a front stage setup to blend the sub into.
Toreador Red 05' FX4
4.0 4x4 A/Tran Ext.Cab Daily Driver. Nomads, BFG M/T's
Alpine 9857, JBL MS-8 DSP, US Acoustics 2x80w & 2x100w, Vifa 1" XT25 Dual Ring Radiator Tweeters 3k+ 24db slope, Dayton Audio 7" RS180-4 Mid-woofers 100Hz-3k 24db slope, 500w rms Kenwood Class-D Mono - JBL 10" GTO1014 Sealed. 100Hz- 12db slope