Tailgate Rattle

[jakenbake]

So I installed a much larger and better sounding subwoofer in my car and it sounds great on the inside, but on the outside the tailgate rattles like crazy with the bass. I am guessing it is from the spoiler since when I rest my hand on it, the rattle stops. The problem is that I cant seem to figure out how to fix it. I looked in the repair manual and the entire tailgate is one giant piece of plastic. It doesn't seem that there is any way to get to the rattle. Has anyone else had this problem and found a solution. It seems to be a problem on the FX as well but I couldn't find an answer to the problem in their forum either.