Someone snarling in old horse-drawn cab (7)
I believe the answer is:
growler
I believe this clue is a double definition.
'someone snarling' is the first definition.
'old horse-drawn cab' is the second definition.
'in' acts as a link.
(Other definitions for growler that I've seen before include "Dog perhaps" , "Iceberg" , "Perhaps bear" , "Unfriendly dog" .)