Singer in rehearsal, tone-deaf (4)
I believe the answer is:
alto
'singer' is the definition.
(alto is a kind of singer)
'in rehearsal tone-deaf' is the wordplay.
'in' says the answer is hidden in the clue.
'ALTO' is hidden within 'rehearsal tone deaf'.
(Other definitions for alto that I've seen before include "The highest adult male singing-voice" , "Member of choir" , "Singing voice between tenor and soprano" , "Counter-tenor or contralto" , "Singing range" .)