Possible Clues:

• Too high to catch?
• Too high for people to catch?
• Like sounds that dogs can hear but most humans cannot
• Like sounds dogs can hear but humans can't
• Court nails suspect without hearing
• Cult's on-air broadcast not heard by us
• Above the limit of human hearing
• Extremists almost put off out of range
• Of high frequency
• Extremist has relative in charge of producing sound