Offensive din surrounds old man at first (7)
I believe the answer is:
noisome
'offensive' is the definition.
(I know that offensive can be written as noisome)
'din surrounds old man at first' is the wordplay.
'din' becomes 'noise' (a din is a noisy disturbance).
'surrounds' is an insertion indicator.
'at first' says to take the initial letters.
The initial letters of 'old man' is 'om'.
'noise' enclosing 'om' is 'NOISOME'.
(Other definitions for noisome that I've seen before include "terribly unpleasant" , "Odious" , "Disgusting to sight or smell" , "Harmful - noxious" , "Odorous" .)