Thrum (verb)

1. Produce a continuous low humming sound.
2. Vibrate with a steady low sound or murmur.

Origin:

Middle english: of imitative origin.

Examples:

1. The bees were thrumming in the flower bed.
2. The guitar was thrumming gently in the background.
3. The engine was thrumming loudly.
4. The wind was thrumming through the trees.
5. The crowd was thrumming with excitement.