I work in data communications and from time to time I give talks about how it works. I would like to build a "Can LAN" composed of two cans and string. I can build the electronics to produce noise at each end but I also want to be able to passively sniff it.
So imagine two soup cans with a guitar string in between. You talk into one can and listen at the other. If you put a guitar pickup next to the string, could you pick up even an indication of sound? I don't need to pick any particular note. I just need an indication that the string is vibrating.
The issue as I see it is that the string is not being used traditionally. In this case the vibrations are being transferred along the length of the string.