Only genre of music that's heard (4)
I believe the answer is:
sole
'only' is the definition.
(I know that only can be written as sole)
'music that's heard' is the wordplay.
'music' becomes 'sol' (I've seen this in another clue).
'that's heard' indicates a 'sounds like' (homophone) clue.
'sol' is a homophone of 'SOLE'.
'genre of' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sole that I've seen before include "Kind of fish - lose it" , "A lone flat fish?" , "O __ Mio (Neapolitan song)" , "Underside of footwear" , "Dover - -" .)