The first trailer show a silhouetted Capaldi with an exploding TARDIS console.
A month later the second preview ask "Am I a good man?" It also confirmed the date of August 23rd for the premiere of the season.
Now just two weeks later, and three weeks before Comic-Con, a third tease sounding like Davros, has appeared. I would not be surprised to see at least on more before something big at the worlds largest geek-fest.