Working with sound isolation for the Navy the noise-vibration-can be lessened by of of two (or both) methods: isolation or increase mass to change the vibration (Noise)wavelengths.
Indeed. The hollow brass body is acting as a sounding board, amplifying the vibrations caused by the wheels on the rails, the same as the hollow body of a stringed instrument amplifies the vibrations of the strings. What is needed is to change the resonance of the body. If the model could use a bit more weight, I bet a couple of those self stick tire weights that some use for weighting cars would help, IF they were stuck to the inside of the body shell rather than the floor.
