My BK XLS200 has an annoying rattle at probably around 40Hz which I can't get rid of. The gain is already set to about 40% & cut-off approx 70hz. I know that nothing is wrong with the kit, I just can't keep the sub on the floor. When I kneel on top of it the rattle is gone and it hits the sweet spots really nicely. I was wondering how others out there deal with this? I have contemplated a paving slab on the top, but I would rather not for cosmetic reasons. I am using the floor spike seated on to discs because I have a wooden floor. I also thought maybe I should think about getting a BFD, if I understand correctly this will even out these huge resonant spots in the output? What should I do???