Terribly upset by the strange sound, though it's wonderful (10)
I believe the answer is:
stupendous
'it's wonderful' is the definition.
(thesaurus)
'terribly upset by the strange sound' is the wordplay.
'terribly' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'the strange' indicates anagramming the letters.
'upset' with letters rearranged gives 'stupe'.
'sound' anagrammed gives 'ndous'.
'stupe'+'ndous'='STUPENDOUS'
'though' is the link.
(Other definitions for stupendous that I've seen before include "Astounding" , "Astoundingly huge" , "Extremely impressive" , "Phenomenal" .)