Turning the key, not making a sound (4)
I believe the answer is:
tone
'a sound' is the definition.
(tone is a kind of sound)
'turning the key not' is the wordplay.
'turning' is a reversal indicator.
'the key' becomes 'e' (I've seen this in other clues**).
'e'+'not'='enot'
'enot' written backwards gives 'TONE'.
'making' is the link.
(Other definitions for tone that I've seen before include "Musical note; general character" , "Quality or character of sound" , "Note; note (anag.)" , "feel" , "Quality of a person's voice" .)