Small missile making a loud noise (8)
I believe the answer is:
strident
'making a loud noise' is the definition.
'small missile' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'missile' becomes 'trident' (I've seen this before).
's'+'trident'='STRIDENT'
(Other definitions for strident that I've seen before include "Unpleasantly rough" , "ear-piercing" , "giving views forcefully" , "harsh sound" , "Harsh, grating" .)