Illegal enterprise making a lot of noise (6)
I believe the answer is:
racket
I believe this clue is a double definition.
'illegal enterprise' is the first definition.
(I've seen this before)
'a lot of noise' is the second definition.
(I've seen this before)
'making' acts as a link.
(Other definitions for racket that I've seen before include "See 1" , "noise pollution" , "Infernal row" , "Uproar" , "Din; snowshoe" .)