You can forget about getting the trunk to stop rattling, once you do the lid, then it's the rear bumper, then the flaps, then...
I totally gave up on the rattling issue, I figured if it sounds good inside, who cares about the outside...dealing with a lot of power and multiple woofers, theres not much you can do. Soundproofing will only add extra weight to the already heavy box in your trunk. The biggest problems I faced were the rear bumper and spoiler believe it or not. I wasn't about to coat the bumper, only to have it sag or fall off from the weight. I have a sealed box, speakers facing front, totally sealed off from the trunk. No noise on the inside, a lot of noise on the outside!
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2000 SE Sport
Deep Navy CC Metallic
Midnight Blue Cloth
Factory wheels are as clean as the day I bought it!