Water balloon sound (5)
I believe the answer is:
splat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">water balloon sound</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for splat that I've seen before include "Noise of soft wet impact; part of a chair back" , "amusing noise" , "Sound of a soft wet landing" , "Noise on landing" , "Wet slapping sound" .)