A beastly noise, but quiet, at least (3)
I believe the answer is:
low
'least' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for low that I've seen before include "Not high or loud" , "Inferior, cow's call" , "Humble; dejected" , "something from Guernsey?" , "Deep sound of cattle - not high" .)