murmuration

noun murmuration

• rumble — to make a deep, heavy, somewhat muffled, continuous sound, as thunder.
• buzz — If something buzzes or buzzes somewhere, it makes a long continuous sound, like the noise a bee makes when it is flying.
• hum — to make a low, continuous, droning sound.
• whisper — to speak with soft, hushed sounds, using the breath, lips, etc., but with no vibration of the vocal cords.
• purr — to utter a low, continuous, murmuring sound expressive of contentment or pleasure, as a cat does.