Small ballistic missile having a harsh sound (8)
I believe the answer is:
strident
'a harsh sound' is the definition.
(I've seen this before)
'small ballistic missile' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'ballistic missile' becomes 'trident' (I've seen this before).
's'+'trident'='STRIDENT'
'having' acts as a link.
(Other definitions for strident that I've seen before include "Loudly assertive" , "Harsh, grating" , "Tumultuous" , "Loud and vociferous" , "harsh noise" .)