batsqueak

noun /ˈbatskwiːk/

a) The ultrasonic noise emitted by a bat, especially as used for echolocation.

Gómez Arias, like don Álvaro, dies without our feeling a batsqueak of regret because neither is given any redeeming features.

b) A faint echo (of something); a tiny pulse, a slight wave (of feeling, emotion etc.).

The first infernal batsqueak of insanity was making itself heard in a new generation.