batsqueak

noun2

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.).

   • Gómez Arias, like don Álvaro, dies without our feeling a batsqueak of regret because neither is given any redeeming features. — 2002