Sound betraying boredom (5)
I believe the answer is:
snore
'sound betraying boredom' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for snore that I've seen before include "Make racous nocturnal sound" , "6 made by sleeper" , "Noise made while asleep" , "thing which bores" , "Make raucous nasal sound during sleep" .)