Sudden loud noise (4)
I believe the answer is:
bang
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sudden loud noise</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for bang that I've seen before include "Sudden noise; fringe" , "Sudden loud noise like an explosion" , "A loud report or a collision" , "Report - something the hairdresser did?" , "Sudden loud noise (often 'big')" .)