batsqueak

Etymology
From.

Noun

 * 1) The ultrasonic noise emitted by a bat, especially as used for echolocation.
 * 2) A faint echo (of something); a tiny pulse, a slight wave (of feeling, emotion etc.).
 * 3) * 2002, Melveena McKendrick, "Men Behaving Badly", Identities in Crisis, Reichenberger 2002, p. 220:
 * Gómez Arias, like don Álvaro, dies without our feeling a batsqueak of regret because neither is given any redeeming features.