Crack core voice, withdrawing over and over again (7)
I believe the answer is:
crevice
'crack' is the definition.
(I know that crack can be written as crevice)
'core voice withdrawing over and over again' is the wordplay.
'withdrawing' indicates named letters should be taken away.
'over and over again' becomes 'oo' (I've seen this in other clues).
'core'+'voice'='corevoice'
'corevoice' with 'oo' taken away is 'CREVICE'.
(Other definitions for crevice that I've seen before include "Narrow crack" , "Split" , "Crack or fissure." , "Narrow rock fissure" , "Opening" .)