That's funny sort of ditch (2-2)
I believe the answer is:
ha-ha
This clue is a double definition.
'that's funny' is the first definition.
(I've seen this before)
'sort of ditch' is the second definition.
(Other definitions for ha-ha that I've seen before include "Sunken barrier" , "Hidden ditch" , "Ditch with wall in it - sounds hilarious" , "Loud laugh" , "Sound of laughter" .)