Hearing organs during rehearsal (4)
I believe the answer is:
ears
'hearing organs' is the definition.
(I've seen this before)
'during rehearsal' is the wordplay.
'during' indicates the answer is hidden within the clue.
'EARS' is hidden in the letters of 'rehearsal'.
(Other definitions for ears that I've seen before include "Sear (anag.)" , "Spikes (of cereals)" , "Lugs (colloq.)" , "Seed-bearing parts of corn" , "Locations for buds or studs?" .)