hum

[1]	buzz , drone , thrum , murmur , whirr , purr , vibrate , (Technical) bombinate/bombilate
[2]	bustle , stir , be active , move briskly , (Colloq) tick (over)
[3]	intone
[4]	seethe

[1]	busyness
[2]	Harkat-ul-Mujahidin , Harkat ul-Ansar , HUA , Harkat ul-Mujahedeen , Al Faran , Movement of Holy Warriors
[3]	humming
[4]	buzz , buzzing , drone , droning , thrum , thrumming , murmur , murmuring , murmuration , whirr , whirring , purr , purring , vibration