Two notes since rewritten, look back (9)
I believe the answer is:
reminisce
'look back' is the definition.
(I've seen this before)
'two notes since rewritten' is the wordplay.
'two notes' becomes 'remi' (I've seen this in another clue).
'rewritten' is an anagram indicator.
'since' with letters rearranged gives 'nisce'.
'remi'+'nisce'='REMINISCE'
(Other definitions for reminisce that I've seen before include "Talk of past events" , "Remember past" , "Think of past events" , "Give account of past" , "Say what one remembers" .)