Number in company excessively audible (3)
I believe the answer is:
two
'number in company' is the definition.
(as in 'two's company, three's a crowd')
'excessively audible' is the wordplay.
'excessively' becomes 'too' (synonyms).
'audible' indicates a 'sounds like' (homophone) clue.
'too' sounds like 'TWO'.
(Other definitions for two that I've seen before include "Company, so it's said" , "Cat's coat" , "1 + 1" , "Company allegedly" , "eg Twins" .)