Sound heard by Bo Peep (3)
I believe the answer is:
baa
'sound heard by bo peep' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for baa that I've seen before include "Cry of a sheep" , "Beastly sound f" , "Sheep's bleat" , "Lamb's cry" , "Call from Jacob" .)