Voicemail signal (4)
I believe the answer is:
tone
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">voicemail signal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tone that I've seen before include "Quality of a person's voice" , "Sound - style" , "Sound signal on a telephone" , "Colour quality; note" , "Quality of a musical or vocal sound" .)