Sewer noise requiring intervention of soldiers (5)
I believe the answer is:
drain
'sewer' is the definition.
(drain can mean a sewer)
'noise requiring intervention of soldiers' is the wordplay.
'noise' becomes 'din' (din can mean a loud noise or disturbance).
'requiring intervention of' indicates putting letters inside.
'soldiers' becomes 'RA' (Royal Artillery).
'din' placed around 'ra' is 'DRAIN'.
(Other definitions for drain that I've seen before include "See 11 dn" , "Wasted down here" , "Filter" , "Exhaust (of liquid)" , "Gutter" .)