Sounded like a duck (7)
I believe the answer is:
quacked
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sounded like a duck</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 quacked that I've seen before include "Made sound like duck" , "Sounded like duck" .)