Related Clues:

• Sound of a contented Siamese
• Pet's contented sound
• Sound from a lynx's larynx
• Well-tuned engine output
• Cat's rumble
• Sing with mouth closed
• Drone or buzz
• Vibration sound
• Operate smoothly
• Hum, as an engine
• Contented pet's sound
• Happy kitty sound
• Engine sound backed up Rolls-Royce
• Reaction to scritches, maybe
• Sound of feline bliss