嘰嘰咕咕

叽叽咕咕
jījigūgū
  1. (onom.) to mutter
  2. to mumble
  3. to whisper

CEDICT

onomatopoeic

Entry Composition

1 嘰 jī grumble
2 嘰 jī grumble
3 咕 gū (onom.) for the sound of a bird, an empty stomach etc
4 咕 gū (onom.) for the sound of a bird, an empty stomach etc