Related Clues:

• Tire leak sound
• Sound issued with an arched back, perhaps
• Let off a little steam
• Grind gauge
• Sound of crowd disapproval
• Fall in drops
• "Boo" accompaniment
• Insomniac irritant
• Faucet annoyance
• Water fall?
• Asp's greeting
• "Boo" follower
• Sound of a defective faucet
• Slo-o-ow leak
• Stereotypical insomnia cause