Alas, travelling after noon is congested, by the sound of it (5)
I believe the answer is:
nasal
'congested by the sound of it' is the definition.
I can't tell whether this defines the answer.
'alas travelling after noon' is the wordplay.
'travelling' indicates anagramming the letters.
'after' is a charade indicator (letters next to each other).
'noon' becomes 'n'.
'alas' is an anagram of 'asal'.
'asal' after 'n' is 'NASAL'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for nasal that I've seen before include "front piece of helmet" , "piece of armour" , "adenoids" , "of a prominent feature" , "Describing some hooter" .)