Notice nothing that causes trouble (3)
I believe the answer is:
ado
'causes trouble' is the definition.
'ado' can be an answer for 'trouble' (both can mean bother or commotion). I'm not certain of the 'causes' bit.
'notice nothing' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'nothing' becomes 'o' (looks like zero - 0).
'ad'+'o'='ADO'
'that' is the link.
Can you help me to learn more?
(Other definitions for ado that I've seen before include "stir" , "excitement" , "Flap" , "Goings-on" , "flapping" .)