Not all of total, we hear (4)
I believe the answer is:
some
'not all of' is the definition.
('some' is the opposite to 'all of')
'total we hear' is the wordplay.
'total' becomes 'sum' (synonyms).
'we hear' indicates a 'sounds like' (homophone) clue.
'sum' is a homophone of 'SOME'.
(Other definitions for some that I've seen before include "Part" , "An unspecified quantity, not all" , "Unknown or unspecified amount or number" , "Several" , "An undetermined number" .)