Honking (7)
I believe the answer is:
tooting
'honking' is the definition.
('toot' can be a synonym of 'honk')
This is all the clue.
(Other definitions for tooting that I've seen before include "... what impatient motorist may be doing" , "somewhere in London?" , "Blowing" , "area south of Wandsworth" , "Showing impatience as driver" .)