Low noise (6)
I believe the answer is:
rumble
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">low 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 rumble that I've seen before include "Sound of thunder or a hungry stomach - discover (plans)" , "Harlem gangs might" , "Make a low noise" , "Tummy sound - discover (an illicit activity)" , "Find out the truth" .)