There's some good information regarding the causes of loudspeaker cabinet vibrations in the following video where Andrew Jones talks to Upscale Audios Kevin Deal about his Elac DBR62 bookshelves.
It begins around the 13 minute mark
https://youtu.be/QgYzfR3Rrb0
It begins around the 13 minute mark
https://youtu.be/QgYzfR3Rrb0