Loud number is by Yankee (5)
I believe the answer is:
noisy
'loud' is the definition.
(associated in meaning)
'number is by yankee' is the wordplay.
'number' becomes 'no' (abbreviation).
'by' means one lot of letters go next to another.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'no'+'is'+'y'='NOISY'
(Other definitions for noisy that I've seen before include "like thirteen [HARD ROCK]" , "ear-piercing maybe!" , "Rowdy" , "Full of disturbing sounds" , "row" .)