Very loud in order to annoy (6)
I believe the answer is:
ruffle
'to annoy' is the definition.
(I know that ruffle is a more specific form of annoy)
'very loud in order' is the wordplay.
'very loud' becomes 'ff' (musical abbreviation for 'fortissimo', very loud).
'in' is an insertion indicator.
'order' becomes 'rule' (order can mean rule or lawfulness).
'ff' placed into 'rule' is 'RUFFLE'.
(Other definitions for ruffle that I've seen before include "Ornamental frill; make disarranged" , "Cause (feathers) to stand up" , "Aggravate" , "Dishevel - annoy" , "Disrupt smooth surface" .)