It’s not turning the key that made the sound (4)
I believe the answer is:
tone
'key that made the sound' is the definition.
'tone' can be an answer for 'key' (thesaurus). I'm not certain of the rest of the definition.
'it's not turning' is the wordplay.
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'turning' says the letters should be written in reverse.
'e'+'not'='enot'
'enot' written backwards gives 'TONE'.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for tone that I've seen before include "Bodily firmness" , "Quality or character of voice" , "Vocal sound of note" , "A pitch of note" , "Colour quality; note" .)