Right about source of sonic boom (7)
I believe the answer is:
prosper
'boom' is the definition.
(synonyms)
'right about source of sonic' is the wordplay.
'right' becomes 'proper' (synonyms).
'about' indicates putting letters inside.
'source of' says to take the initial letters.
The initial letter of 'sonic' is 's'.
'proper' going around 's' is 'PROSPER'.
(Other definitions for prosper that I've seen before include "Make good" , "like Merimee, nominally" , "Get rich" , "Thrive, boom" , "Go well" .)