hum

To make a sound you can make in your throat with your mouth closed. Often, this is done to make music without singing words.

Example: I used to hum the music from the Indiana Jones movies when I was a child.

A similar sound, such as one from a machine.

Example: The engine hummed as he started drove the car.

Hum is the sound of humming, or a sound like humming.

Example: I heard a low hum from the other room.