That's what is meant by the term noisy image. You heard lots of rapid clicking, and the speed of the clicks changed as the speed of the motors changed. If you look in the vent holes of some appliances, you can even see sparking as it happens. The invention of the radio happened after people began paying attention to sparks and what they do. If you invent a code, You Can send messages to your friends on Zen radio with an appliance.
Radiation means when something radiates from one location outward - like light from a light bulb.
Not all radiation is unsafe. The dangerous kind, the kind we usually call radioactivity, is called ionizing radiation.