"Sone" is the term used in the industry to describe how loud a bath fan is. The lower the number, the quieter the fan will be. "Typical bath fans range anywhere from 0.3 sones to 6.0 sones," Jones ...
Regularly inspect your fan for any clogs that may require a professional to remove. Dealing with a noisy bathroom exhaust fan or reduced airflow? Then professional maintenance may be in order.