Number that's loud also heard (5-3)
I believe the answer is:
forty-two
'number' is the definition.
I know nothing about this answer so I can't judge whether this works.
'loud also heard' is the wordplay.
'loud' becomes 'forty' (I am not sure about this - if you are sure you should believe this answer much more).
'also' becomes 'too' (synonyms).
'heard' indicates a 'sounds like' (homophone) clue.
'too' sounds like 'two'.
'forty'+'two'='FORTY-TWO'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for forty-two that I've seen before include "Douglas Adams' numerical Answer to Life, The Universe and Everything" , "Three fourteens" , "The answer to the Ultimate Question of Life, the Universe, and Everything (Hitchhikers Guide to the Galaxy)" .)