Go mad at loud impudence (4)
I believe the answer is:
flip
'go mad' is the definition.
(to flip is to become very angry suddenly)
'at loud impudence' is the wordplay.
'at' is a charade indicator (letters next to each other).
'loud' becomes 'f' (short for forte - 'loud' in music).
'impudence' becomes 'lip' (lip is a kind of impudence).
'f'+'lip' is 'FLIP'.
(Other definitions for flip that I've seen before include "Somersault - glib - hot drink" , "Spin in the air" , "Show great anger - . . . . your lid" , "Toss or flick in the air" , "Go crazy - other side" .)