Scrap part of audiotape (4)
I believe the answer is:
iota
'scrap' is the definition.
(both can mean a very small amount)
'part of audiotape' is the wordplay.
'part of' indicates a hidden word.
'IOTA' is hidden within 'audiotape'.
(Other definitions for iota that I've seen before include "(Not one) little bit" , "European letter" , "Just a jot, from Greek alphabet" , "Ninthe letter of the Greek alphabet" , "Contrivance" .)