Originally Posted by bmw325i
Face your subs towards the front and seal off the trunk. No more rattles at all.
I've had this setup for a few months already and I finally got around to building the front baffle. I still need to roundover the port holes and upholster it. The front baffle is held in by neodymium magnets. The box is just a 36x14x16 (WxHxD) prefabbed box and its a tight fit in there on its own. The subs are 2 Alpine SWR 12D4's powered by an Audioque 2200d.
I don't have folding seats or a ski pass in my E90. Currently just using a standard ported box (woofer facing upwards, port towards the back of car), but will be getting a custom enclosure built in the spare wheel area soon.