Loudness of a little number is in character (9)
I believe the answer is:
noisiness
'loudness' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Maybe there's a link between them I don't understand?
'a little number is in character' is the wordplay.
'a little number' becomes 'no' (abbreviated form of 'number').
'character' becomes 'ess' (the letter S).
'no'+'is'+'in'+'ess'='NOISINESS'
'of' is the link.
Can you help me to learn more?
(Other definitions for noisiness that I've seen before include "The racket" , "Decibel reading" , "conspicuous quality" , "Clamour" .)