Related Clues:

• Go on (and on, and on ...)
• Queen's mate
• Unchanging intonation
• Ambient sound
• Sing, as a Gregorian chant
• Long hum
• Talk in a monotonous voice
• Go on monotonously
• Remote-controlled plane
• Recite a mantra
• Mindless worker
• Monotone
• Ongoing monotone
• Chant monotonously
• Speak hypnotically