An Odd Question

moving things around in listening room is a great tweak, sometimes surprising changes...

I would imagine they would act like Helmholtz resonators.  I have heard and believe a story of Klipschorn cabinets being used as effective bass traps.

Possible effect I believe would be to pull out those frequencies, but generally, I believe and stand to be corrected, the small mouth openings would minimize this effect.

Why not ask guitarsam, he knows everything

When I turn on my stereo,my guitar starts playing along. (Cue up spooky music!!!)

+1 onhwy61. I have a guitar in my room and do not notice it in the listing spot. But I am sure if I go over to it with some music on it will resonate a little. I know because I have heard a piano do it before. A piano I think is a bigger culprit.