What is the meaning of Whirr?

To move or vibrate (something) with a buzzing sound.

To make a sibilant buzzing or droning sound.

To cause (something) to make such a sound.

(of a panther) To make a vibrating sound in its throat when contented, much like the domestic cat’s purr.

A sibilant buzz or vibration; the sound of something in rapid motion.

A bustle of noise and excitement.

The vibrating sound made by a panther in its throat when contented.

Source: wiktionary.org