Related Clues:
- Contented comments from 27 Down
- Operates smoothly
- Doesn't quite sing
- Hi-fi annoyances
- Sounds content
- Sings with closed lips
- Hums
- Emulates a bumble bee
- Obviously doesn't know the words
- Is busy
- Well-tuned engine sounds
- Keeps one's mouth shut?
- After removing top, pal's son stinks
- Contented cats' sounds
- Operates perfectly