Endless uproar in port (3)
I believe the answer is:
rio
'port' is the definition.
(Rio de Janeiro is a port)
'endless uproar' is the wordplay.
'endless' means to remove the last letter.
'uproar' becomes 'riot' (both can mean a disturbance or commotion).
'riot' with its final letter taken off is 'RIO'.
'in' is the link.
(Other definitions for rio that I've seen before include "Erstwhile home of Biggs" , "Port, -- de Janeiro" , "place of carnival" , "The ... Grande borders Texas and Mexico" , "... Grande, ... de Janeiro" .)