Related Clues:

• Sing with a closed mouth
• Smell and sound of bees
• Smooth machinery sound
• Half the people on earth smell
• Sound of a bumble bee
• Buzz; stink
• Thrill; bee's sound
• Well-tuned engine output
• Sing with mouth closed
• Drone or buzz
• Vibration sound
• Operate smoothly
• Drone — bustle
• Bees make it
• Sense of excitement