Go lower and lower (4,4)
I believe the answer is:
turn down
'lower' is the definition.
('turn down' can be a synonym of 'lower')
'go lower' is the wordplay.
'go' becomes 'turn' ('turn' can be a synonym of 'go'**).
'lower' becomes 'down' ('down' can be a synonym of 'lower').
'turn'+'down'='TURN-DOWN'
'and' is the link.
(Other definitions for turn down that I've seen before include "Lower volume" , "mark the place" , "Reject - reduce volume" , "Spurn" , "prepare bed" .)