Refuse to reduce volume (4,4)
I believe the answer is:
turn down
This clue is a double definition.
'refuse' is the first definition.
(to turn down an offer is to refuse it)
'reduce volume' is the second definition.
(I've seen this before)
'to' is the link.
(Other definitions for turn down that I've seen before include "Refuse - to reduce the volume" , "Lower volume" , "mark the place" , "Spurn" , "prepare bed" .)