Incubator sound (5)
I believe the answer is:
cheep
'incubator sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cheep that I've seen before include "High-pitched sound" , "Sing like a bird" , "Bird noise" , "Weak cry of young bird" , "Cry of new-born chick" .)