Sing like Bing (5)
I believe the answer is:
croon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sing like bing</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for croon that I've seen before include "Sing softly" , "Sing like Bing" , "Sing in a soft low tone" , "Sing with a soft voice" .)