Why do microwave ovens have a fan?

A microwave has a fan to help keep its power components from overheating. Some units are combination convection ovens and microwaves, and have fans in the oven cavity to circulate air when in convection mode. read more

Over-the-range microwaves have a light and fan built into the bottom of the appliance. After the smoke and steam are removed, the filtered fan vents the air outside your home or cleans it before releasing it back into the kitchen. read more

Short Answer: Due to some of the components (e.g, the magnetron and cooling fan) required to cool and power the microwave, noise is almost unavoidable, and while a silent microwave is possible, it would be significantly more expensive to produce. read more