You can't really fix a box fan's noise — but here's the closest you'll get

The noise of a box fan comes from the blades chopping air and the motor vibrating everything around it, and there’s no way to silence that without losing airflow.

Box fans are simple machines. The same blades that push air also create turbulence and whine. The motor hums because it’s cheap and direct-drive. You can’t fix physics with a hack.

What you can do is change the character of the noise so it bothers you less.

• Put the fan on a rug or rubber mat. That kills vibration transfer to the floor, which stops that low-frequency rumbling through the house.
• Tighten every screw. Loose plastic rattles at certain speeds. Check the grille, the base, the motor mount.
• Clean the blades. Dust