Related Clues:

• Undertone
• Whisper
• Soft sound
• Speak softly
• Brook sound
• Cooing sound
• Speak in a low tone
• Complain, in a way
• Mutter
• Speak in low voice
• Low continuous sound
• Speak in a low voice, whisper
• Low, continuous sound
• Abnormal sound made by heart
• Low, indistinct speech