Sound astonished to find new gaps (4)
I believe the answer is:
gasp
'sound' is the definition.
(I have seen 'Sound of astonishment' mean 'gasp' so perhaps 'sound' could also mean 'gasp')
'new gaps' is the wordplay.
'new' is an anagram indicator.
'gaps' anagrammed gives 'GASP'.
'astonished to find' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for gasp that I've seen before include "Sound of astonishment" , "First Greek letter" , "Convulsive breath" , "Show amazement" , "Catch one's breath in astonishment" .)