I can't wait for rumble that's taking place (4,2)
I believe the answer is:
roll on
'i can't wait' is the definition.
('roll on Friday' means 'I can't wait for Friday')
'rumble that's taking place' is the wordplay.
'rumble' becomes 'roll' (both can mean to make a deep noise).
'that's taking place' becomes 'on' (as in a phrase like 'the event is on now').
'roll'+'on'='ROLL-ON'
'for' is the link.
(Other definitions for roll on that I've seen before include "Come quickly!" , "arrive quickly!" , "Deodorant or cosmetic" , "Style of deodorant" , "Presumably to board ferry" .)