Why does the MRI machine make a knocking sound?
The system has several different pieces of equipment that are hidden under the covers. Some of these are loops of wires that are imbedded in a very hard plastic material. These wire loops emit a radio frequency that, together with the powerful magnet, take the MRI picture. The radio frequency turns on and off very quickly, approximately every four milliseconds. Because this is so fast, the wires vibrate in the hard plastic and cause the knocking sound.
