Sultan upset, alas, by excessive noise (7)
I believe the answer is:
saladin
'sultan' is the definition.
(12th-century sultan)
'upset alas by excessive noise' is the wordplay.
'upset' says the letters should be written in reverse.
'by' means one lot of letters go next to another.
'excessive noise' becomes 'din' (din can mean a loud noise or disturbance. I am not sure about the 'excessive' bit.).
'alas' written backwards gives 'sala'.
'sala'+'din'='SALADIN'
Can you help me to learn more?
(Other definitions for saladin that I've seen before include "Old sultan" , "Richard's opponent" , "Crusade warrior" , "Sultan who fought the Crusaders" , "Richard's enemy" .)