Talk excitedly (4)
'talk excitedly' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rave that I've seen before include "Talk with extreme enthusiasm or wild delirium" , "Talk wildly in modern youth dance" , "modern dance music" , "Laudatory sort of review - quite a rant" , "Illegal party; talk madly" .)
(Other definitions for yabber that I've seen before include "rabbit on" , "Conversation in Sydney" , "Chatter" .)