Nighttime noise
I believe the answer is:
snore
'nighttime noise' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for snore that I've seen before include "Make noises sleeping" , "Noise indicating sleep" , "How to keep someone awake while sleeping?" , "Sound made by sleeper" , "Make raucous nasal sound during sleep" .)