Get irritated about loud weapon (5)
I believe the answer is:
rifle
'weapon' is the definition.
(rifle is a kind of weapon)
'get irritated about loud' is the wordplay.
'get irritated' becomes 'rile' (to rile is to anger or irritate).
'about' indicates putting letters inside.
'loud' becomes 'f' (short for forte - 'loud' in music).
'rile' enclosing 'f' is 'RIFLE'.
(Other definitions for rifle that I've seen before include "Carbine" , "Flier (anag.)" , "Strip - firearm" , "Search and rob - with long gun?" , "Ransack - firearm" .)