Talk non-stop (7)
(Other definitions for express that I've seen before include "Verbalise - train" , "High-speed; specific" , "Squeeze out - speak" , "Put into words - fast" , "Squeeze out - quick" .)
(Other definitions for chatter that I've seen before include "Talk rapidly" , "Prattle" , "Rabbit on" , "Talk idly" , "Trivial conversation" .)