First movement if loud is seen to irritate (4)
I believe the answer is:
'to irritate' is the definition.
(I've seen this in another clue)
'first movement if loud' is the wordplay.
'first movement' becomes 'm' (1st letter of 'movement').
'loud' becomes 'f' (short for forte - 'loud' in music).
'is seen' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for miff that I've seen before include "Wind up" , "Put in a bad mood" , "Take offence" , "Annoy - offend" , "causes resentment" .)