The term 'SOUND OF A FAN' can be broken down into three crossword solutions: HUM (3 letters), WHIR (4 letters), and RAH (3 letters). The sound of a fan is typically a low humming noise, which is represented by the solution HUM. WHIR is a more high-pitched sound that is often associated with the sound of a fan. Finally, RAH is a sound that is sometimes heard when a fan is running at a higher speed. All together, these three solutions represent the various sounds that a fan can make.