Loud note played outside regularly (5)
I believe the answer is:
Here is my best explanation:
'regularly' is the definition.
(I've seen this before)
'loud note played outside' is the subsidiary indication.
'loud' becomes 'f' (A musical term).
'played' indicates an anagram.
'outside' indicates putting letters inside.
'note' with letters rearranged gives 'oten'.
'f' put inside 'oten' is 'often'.
(Other definitions for often that I've seen before include "Again and again", "Perhaps daily", "Repeatedly with regularity", "More than occasionally", "Multiply", "occurring with frequency", "Quite frequently", "Frequently, at short intervals", "Repeatedly, many times" and "A lot".)