Expression of annoyance? (3-3)
I believe the answer is:
'expression of annoyance?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tut-tut that I've seen before include "Disapproving sound" , "Word of disapproval" , "Repetitive exclamation of annoyance or rebuke" , "Expression of disapproval - a repetitive palindrome" , "Interjection of disapproval" .)