Left after farm animal's unpleasant noise (5)
I believe the answer is:
growl
'animal's unpleasant noise' is the definition.
(noise made by an animal)
'left after farm' is the wordplay.
'left' becomes 'l' (common abbreviation).
'after' says to put letters next to each other.
'farm' becomes 'grow' (synonyms).
'l' after 'grow' is 'GROWL'.
(Other definitions for growl that I've seen before include "Hostile dog's noise" , "Surly grumble" , "Make an aggressive sound" , "Sound like hostile or angry dog" , "Show aggression as boxer" .)