Against hearing sound of relative? (4)
I believe the answer is:
anti
'against' is the definition.
(prefix meaning against)
'hearing sound of relative?' is the wordplay.
'hearing sound of' shows a homophone (sound like).
'relative?' becomes 'auntie' (auntie is a kind of relative).
'auntie' sounds like 'ANTI'.
(Other definitions for anti that I've seen before include "Opposition member" , "'No' voter" , "Person opposed" , "on the other side" , "not favoured" .)