'Any kind of disturbance' probably is talking about what you would normally encounter. To be properly shielded, you need a proper 'faraday cage'. I had to use one when I was carrying out leakage current measurements for my Masters. I was measuring currents of the order of nano - pico, and in the lab there were sooo many sources of noise.
E/m noise is all around us in this technological age. Strip lights oscillating, monitors/TV screens, two massive peaks in the e/m spectrum from any nearby mobile phone masts ... :-o
