The chap's so loveless that there's audible disapproval (4)
I believe the answer is:
hiss
'disapproval' is the definition.
(I have seen 'Express disapproval ' mean 'hiss' so perhaps 'disapproval' could also mean 'hiss')
'the chap's so loveless that there's audible' is the wordplay.
I cannot really understand how this works, but
'chap' could be 'hi' and 'hi' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hiss that I've seen before include "showing contempt?" , "Show disapproval" , "Snake's sibilant sound" , "Boo" , "Make sibilant sound of disapproval as at villain" .)