Related Clues:

• The sound of silence
• 'Pipe down!'
• Quiet
• 'Cut that out!'
• 'Be still!'
• Library sound
• 'That's enough!'
• 'Stop it!'
• 'Stop your gabbin'!'
• Middle of the quip, with 37-Across
• Silence
• Surprise party admonition
• Theater admonition
• 'Quit it!'
• Be quiet