Two billion found in bundle? Go on (6)
I believe the answer is:
babble
'go on' is the definition.
(thesaurus)
'two billion found in bundle?' is the wordplay.
'two' says to double the letters.
'billion' becomes 'b'.
'found in' indicates putting letters inside.
'bundle?' becomes 'bale' (bale is a kind of bundle).
'b' doubled is 'bb'.
'bb' inserted within 'bale' is 'BABBLE'.
(Other definitions for babble that I've seen before include "Chatter in thoughtless way - like brook?" , "Chatter thoughtlessly like brook?" , "Region of S. Germany" , "Continuous noisy talk" , "Talk foolishly" .)