Animal sound ultimately familiar in sea inlet (4)
I believe the answer is:
bray
'animal sound' is the definition.
(I've seen this in another clue)
'ultimately familiar in sea inlet' is the wordplay.
'ultimately' says to take the final letters.
'in' means one lot of letters goes inside another.
'sea inlet' becomes 'bay' (I've seen this in another clue).
The last letter of 'familiar' is 'r'.
'r' put into 'bay' is 'BRAY'.
(Other definitions for bray that I've seen before include "Ass call" , "Proclaim loudly" , "Cry like a donkey" , "Cry of animal" , "where musical vicar lived" .)