Muttering (6)
I believe the answer is:
murmur
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">muttering</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that muttering can be written as murmur)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for murmur that I've seen before include "Speak in a low voice, whisper" , "Little noise" , "Low background noise" , "Quietly spoken utterance; heart defect" , "Abnormal sound made by heart" .)