Well I just read up on what an exciter is (
https://www.daytonaudio.com/topic/excitersbuyerguide). Interesting concept. While most are too big for H0 the bone conducting one would possibly fit into many models. Might be worth an experiment one day.
Anyway, my guess, going by the documentation is that the shell isn't rigid enough. Stiffening it with some more layers of styrene where the exciter would be mounted might have made it better. I see more experimenting on your horizon.
Good to see it all going.
- Tim