Related Clues:

• Undertone
• Whisper
• Soft sound
• Grumble
• Speak unclearly
• Not say clearly
• Speak softly
• Brook sound
• Speak indistinctly
• Under-one's-breath sound
• Lack of energy
• Speak under one's breath
• Talk indistinctly
• Cooing sound
• [Grumble, grumble, grumble]