Related Clues:

• Quiet!
• ''Zip it!''
• Librarian's reminder
• 'Don't let them hear us!'
• "Stop your yakking!"
• Volume control?
• "Cut out the racket!"
• 'Stop talking!'
• "Too noisy!"
• Audible silencer
• Peremptory signal
• Quiet "Quiet!"
• ''Put a sock in it!''
• "That's enough from you!"
• Warning that often precedes 17-, 30-, 49- and 65-Across