Fan Engineers: What factors determine how quiet a given fan design is?

I need the help of the fanors, the fan engineering experts here. As a fanee, I lack the fanors’ knowledge of noise to CFM relationship, and design specifics; so I need your help understanding this conundrum.

We have 3 fans. One is a rectangular box that draws air in through a 9½ by 6 inch grill and a filter on its wide side, and blows it out through a 9 sq. inch outlet on it’s end. It moves the least air and makes by far the most noise.

We have a second circular fan on a small pedestal mount. It is 8 inches in diameter, moves a decent amount of air (way more than the filtering fan) and is less noisy.

Finally, we have an 18 inch square box fan we can set in a window or on the floor. It moves by far the most air, and is whisper quiet. On high, it is quieter than the small filtering fan on its lowest setting. What, aside from it’s CFM rating, makes one fan so much noisier than another?