Loud note played outside, frequently (5)
I believe the answer is:
often
'frequently' is the definition.
(synonyms)
'loud note played outside' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'played' indicates an anagram (letters playing around).
'outside' indicates putting letters inside (some letters go outside others).
'note' anagrammed gives 'oten'.
'f' inserted into 'oten' is 'OFTEN'.
(Other definitions for often that I've seen before include "Frequent" , "Quite frequently" , "Much of the time" , "A lot" , "occurring with frequency" .)