plip-plop
/ˈˌplɪpˈˌplɒp/noun
A rhythmic sequence of light tapping, popping, or splashing sounds.
exclamation
Representing such a rhythmic sequence of light sounds.
Origin
1950s; earliest use found in John o' London's. From plip + plop, after similar imitative compounds formed by reduplication with variation of vowel.