Which one of the following is not a  source of noise pollution?

Noise pollution refers to any sound that is loud, disruptive, or unwanted.

Aroma diffusers in homes are not a source of noise pollution because they do not produce sound at a level that can be considered disruptive or harmful to human health. Aroma diffusers work by emitting scented oils or mist into the air, and the operation of these devices typically produces a very low level of sound, often not even noticeable to human ears.