Related Clues:

• Accompaniment to lip-syncing?
• Vocaphone
• Instrument that's not seen and not heard
• Very easy instrument to play
• Instrument for the musically challenged
• Jug-band instrument
• Agreed to go round Australia with a back-up instrument
• Toy-like instrument into which one hums
• Imaginary instrument played by rock fans!
• Instrument honored in a Beaufort, South Carolina, museum
• Buzz source
• Instrument for the musically inept, maybe
• Buzz generator
• Instrument "played" for a hairbrush microphone user
• Sung-into instrument