whirr

Short definition from Wiktionary

Verb

1. 1
   To move or vibrate (something) with a buzzing sound.
2. 2
   To make a sibilant buzzing or droning sound.
3. 3
   To cause (something) to make such a sound.
4. 4
   (of a panther) To make a vibrating sound in its throat when contented, much like the domestic cat’s purr.

Noun

1. 1
   A sibilant buzz or vibration; the sound of something in rapid motion.
2. 2
   A bustle of noise and excitement.
3. 3
   The vibrating sound made by a panther in its throat when contented.