Noise at midnight made by vacuous hearty in boat (6)
I believe the answer is:
dinghy
'boat' is the definition.
(type of boat)
'noise at midnight made by vacuous hearty' is the wordplay.
'noise' becomes 'din' (din can mean a loud noise or disturbance).
'at' means one lot of letters go next to another.
'midnight' becomes 'g' (the middle letter in 'night').
'made by' means one lot of letters go next to another (letters written or made by another set of letters).
'vacuous' says to hollow out the word (remove centre letters).
'hearty' with its middle removed is 'hy'.
'din'+'g'+'hy'='DINGHY'
'in' is the link.
(Other definitions for dinghy that I've seen before include "vessel" , "Small open boat, maybe a rubber inflatable" , "Small rowing or sailing boat" , "Light rowing boat" , "craft" .)