Answer: ssss

AnswerCrossword Clue
SSSSSound of a slow leak
SSSSAir hose sound
SSSSFlat tire indicator
SSSSBacon sizzle
SSSSDeflation indicator
SSSSDeflation indication
SSSSAlarming sound for a hot air balloonist
SSSSLeaky tire sound
SSSSAsp's sibilance
SSSSScary sound for a balloonist
SSSSSounds from a snake pit?
SSSSNot a good sound for a balloonist
SSSSSound from a snake pit
SSSSLeaky radiator sound
SSSSAir-leak sound
SSSSFlat sound?
SSSSSound before going flat
SSSSPlurals sometimes
SSSSWhat a balloonist hates to hear
SSSSFrightening sound for a balloonist
SSSSRadiator or kettle sound
SSSSWhat's missing from the theme entries
SSSSDeflating sound
SSSSSnake's warning
SSSSSteam sound
SSSSFlat sound
SSSSSlow-leak sound
SSSSSound from a leaky tire
SSSSSound of an air leak
SSSSPuncture sound
SSSSSound of a leak
SSSSSound of air escaping
SSSSWorrisome sound for a balloonist
SSSSSlow leak's sound
SSSSIndication of deflation
SSSSBad news to a balloonist?
SSSSTire-leak sound
SSSSRadiator sound
SSSSUnwelcome boarding-pass marking
SSSSUnwelcome sound to a driver