咔嗒

kādā
  1. (onom.) click
  2. clatter

CEDICT

onomatopoeic

Entry Composition

1 咔 kǎ (used as phonetic "ka")
=2 嗒 dā (onom.) used in words that describe machine gunfire, the ticking of a clock or the clatter of horse hooves etc
=2 嗒 da

synonym of 了 (“used after a verb to indicate perfective aspect”)