I just wonder... When I installed 2 subs for my home theater, I spent weeks trying to find all the bits and pieces that were humming and rattling in the walls, ceilings etc. Drove me nuts for the first while. And it wasn't the HUGE booms that do it, it was certain frequencies. The big booms would affect the doorframes 2 stories up (the system is in the basement). If the doors were closed up there, they would hum if the bass got crazy. My wife was screaming about it, and humming and screaming is a horrible combination!
Point is, if these things are designed to shake instead of make sound, it might be even worse than what I had...although I'm sure they wouldn't shake doors 2 levels away (?). Just a thought!