Something in my room seems to resonate at frequencies in the range 430-475 Hz. Any idea what might be causing it? Would I be looking for a chamber only 15-16 inches wide? Or is it possible that the fundamental resonant frequency is lower but I'm hearing a higher overtone more? Or, should I be looking for a solid object? Or, is it all in my head? I hear the resonance most clearly not when my stereo is playing, but when it's very quiet and there's appliance noise or machinery outside.

Thanks very much!

David