Quiet sound of sheep (not black) in fold (5)
I believe the answer is:
pleat
'fold' is the definition.
(pleating is a kind of folding)
'quiet sound of sheep not black' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'sound of sheep' becomes 'bleat' (noise made by a sheep).
'not' suggests deleting specific letters.
'black' becomes 'b' (abbreviation as in pencil classifications).
'bleat' with 'b' taken out is 'leat'.
'p'+'leat'='PLEAT'
'in' acts as a link.
(Other definitions for pleat that I've seen before include "Type of fold in fabric" , "Flat fold of cloth" , "work on skirt?" , "Leapt (anag)" , "Fold sewn or pressed into cloth" .)