Related Clues:
- Sound (of business?)
- Drone — stink
- Fail to know the words, maybe
- Sign of smooth operation
- Sing with lips closed
- Smooth engine sound
- Low murmur
- Hushed sound
- Boatman's spirit rises again with gentle talk
- Play the kazoo
- Steady drone
- Beehive sound
- Quietly grumble, rejecting drink twice
- Sound of busy activity
- Soft voices (of discontent)