Quick look, or a small sound (4)
I believe the answer is:
peep
I believe this is a double definition.
'quick look' is the first definition.
(I've seen this in another clue)
'a small sound' is the second definition.
(I've seen this in another clue)
(Other definitions for peep that I've seen before include "Look secretly" , "Sly look (palindrome)" , "Look furtively (either way)" , "Furtive look" , "Spy" .)