Exclamation of rebuke (3-3)
I believe the answer is:
tut-tut
'exclamation of rebuke' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tut-tut that I've seen before include "Words of disapproval" , "Sounds of disapproval" , "Naughty, naughty!" , "Expression of disapproval - a repetitive palindrome" , "That's bad" .)