Complaint always loud in the Boleyn castle (3,5)
I believe the answer is:
hay fever
'complaint' is the definition.
(medical complaint)
'always loud in the boleyn castle' is the wordplay.
'always' becomes 'ay'.
'loud' becomes 'f' (short for forte - 'loud' in music).
'in' is an insertion indicator.
'the boleyn castle' becomes 'hever' (Anne Boleyn's family owned Hever Castle).
'ay'+'f'='ayf'
'ayf' going into 'hever' is 'HAY-FEVER'.
(Other definitions for hay fever that I've seen before include "Heavy ref with sneezing ailment" , "summer glums?" , "Coward play" , "Coward created this" , "Allergy caused by pollen, dust etc" .)