After oracle goes mad, very loudly leave (5,3)
I believe the answer is:
clear off
'leave' is the definition.
(I've seen this before)
'after oracle goes mad very loudly' is the wordplay.
'after' is a charade indicator (letters next to each other).
'goes mad' indicates anagramming the letters.
'very loudly' becomes 'ff' (short for fortissimo, 'very loud' in music).
'oracle' is an anagram of 'clearo'.
'clearo' next to 'ff' is 'CLEAR OFF'.
(Other definitions for clear off that I've seen before include "Run along!" , "Leave" , "Skedaddle" , "Begone (colloq.)" , "Go away - transparently" .)