I know nothing about this (what a way to start a post
), but it seems like the natural vibration of the electric cables is exciting your room at some natural frequency. It seems that ways to avoid this is to change the input frequency (can't do that) or change the stiffness/mass of the room to move that natural frequency node away from 60Hz.
In the engineering world, this is actually a common problem. I've worked on projects where we had to consider the frequencies of the shuttle engines and also C-130 engines and design the structure's modal frequencies to avoid coupling. Of course, designing a structure out of aluminum and changing it's frequency is easier than a room in an old house.