一瓶子不響，半瓶子晃蕩 [－－－－响－－－－－荡]

Jyutping
Pinyin yī píng zi bù xiǎng , bàn píng zi huàng dang

Definitions (CC-CEDICT)
  1. lit. a full bottle makes no sound; a half-filled bottle sloshes (idiom)
  2. fig. empty vessels make the most noise