While you are inside the scanner, the various clicking, buzzing and vibration noises that you hear are produced by magnetic field gradient coils that localize the information inside your body and produces images. It is important to keep still while you hear these noises throughout the exam, or else the images produced will be distorted or blurred. The technologist should advise you when it is ok to move or adjust your position, such as during the quiet period in between imaging sequences. While imaging is taking place, it is generally ok to make small movements using parts of your body not in the imaging field, such as toes or fingers during a head or body exam.
Answered by WGATE