Possible Clues:

• Sound to cover expletive in unforgettable episode
• Short high tone as a signal or warning
• Curse substitution
• Response to an air offensive?
• Signal swimmer in lead to return
• 'Censored' sound
• Five-letter word that replaces a four-letter word?
• Censor turns up all skin and bone - from the start
• Sound that might replace a curse word
• High-pitched electronic noise