If there are real acoustic changes it's due to reflections off the enclosure or resonances in it and not any differences in vibrations unless you have microphonic tubes.
You could take the door off and cut bigger holes in the sides, put 4" type 704 rigid fiberglass in front of it and to the sides (this is available commercially with wife-friendly prints), or move it somewhere farther from the speakers.
You could take the door off and cut bigger holes in the sides, put 4" type 704 rigid fiberglass in front of it and to the sides (this is available commercially with wife-friendly prints), or move it somewhere farther from the speakers.