Check room wall and bookshelf panels for sympathetic vibrations. This is one of the most troublesome issues I find. Shelves sometimes buzz, and cabinets with closing doors sometimes vibrate door against stop. Do something to preload the panels that make your shelves back walls and see if you can find ones that are making noise. Chances are, you'll find a lot of things in your home that buzz when vibrated. The different woofers and setup may energize them differently and make it more noticeable.