Hi Mark,
those of us of a certain age remember the tag line of the first Alien film.
I’m not suggesting you use that as your prompt! Scare the wits out of me when I eventually got around to seeing the film.
You have described an engaging task, and one that the children can extend with their own understanding coming into play. Once they find out that sound can travel through materials they can explore different materials that absorb or more clearly transmit sounds.
From Curious Minds you can find: