Posting that's trouble in China (7)
I believe the answer is:
mailing
'posting' is the definition.
('mail' can be a synonym of 'post')
'trouble in china' is the wordplay.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble'**).
'in' is an insertion indicator.
'china' becomes 'ming' (I've seen this before).
'ail' put within 'ming' is 'MAILING'.
'that's' acts as a link.
(Other definitions for mailing that I've seen before include "Sending by post" , "Posting" , "Dispatch by post" , "Sending a message" .)