Noise that will tell you there's a baby about (6)
I believe the answer is:
rattle
'noise' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rattle that I've seen before include "worry" , "making one upset" , "Baby's toy; sound of loose part" , "Gurgling sound in throat" , "cause nervousness" .)