Carried on working unnoticed (9)
I believe the answer is:
continued
'carried on' is the definition.
(to continue is to carry on doing something)
'working unnoticed' is the wordplay.
'working' indicates an anagram.
'unnoticed' with letters rearranged gives 'CONTINUED'.
(Other definitions for continued that I've seen before include "Went on being unnoticed" , "Carried on" , "kept going" , "Unnoticed (anag.)" , "Persisted; resumed" .)