Noisome and discordant duo is holding no score (6)
I believe the answer is:
odious
'noisome' is the definition.
(thesaurus)
'duo is holding no score' is the wordplay.
'holding' is a charade indicator (letters next to each other).
'no' becomes 'O' (resembles 0 - 'no' can mean 'zero').
'score' is an anagram indicator (I've seen 'scored' mean this).
'duo'+'is'+'o'='duoiso'
'duoiso' is an anagram of 'ODIOUS'.
'and discordant' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for odious that I've seen before include "Really obnoxious, generally disliked" , "Vile" , "Really hateful, abhorrent" , "Detestable, execrable" , "Replusive, abhorrent (6)" .)