Buzzing from sub?, I'm getting an annoying buzz with my new custom sealed box Options

[Noahwhite2014]

So I made a sealed box that takes up the inside of the spare tire well and has a false floor baffle flush with the rear seats in the down position. The volume on the interior is around 2.85 cubic feet and there is cushion foam lining the floor pan in the back. The whole box is bolted down to the spare tire tie down hole and that is also the ground point I'm using for the amp. Here's a picture of it.

Looks great and sounds great, but at certain frequencies I get a buzz from my plastics in the back. I believe it's also buzzing the bumper and license plate bezel (not the license plate itself since it has a rubber "anti vibration" frame.

Anyone have a good way to quiet that crap down? Lol

[Noahwhite2014]

Thanks for the replies! I Forgot to mention I have dynamat lining my entire rear interior , my interior plastics I know is one issue since I can't get them attached properly for some reason. Im probably going to be picking up a parts car soon so I'll swap the entire interior plastics over and verify all clips are there. Anyone know if lining the plastic with a thin layer of insulation spray foam helps? If not I'll just get some felt and put it in between wherever metal and plastic contacts and plastic and plastic contacts. My bumper is really secure, but I'll double check again. I'm thinking a sponge between the license plate bezel and the car and between the bumper and the bezel should help a bunch!:)

Let me know what you guys think of that plan if it'll work or not all in all not including the parts car cost it'll probably be less than $20 since I have most of everything I need haha!