I just realised that they updated the main page of elderscrolls, to be specific Alduins Wall. Now there are different dragon shouts audible depending where you are on the wall. For example: Stay a while at the spot where Dovakhiin is located and you here a different dragon shout. It's also like this with other spots on the wall!
Wow that was a nice catch. /applause
So I guess that the sound you here in the trailer that the dragon makes when it spits fire is the dragon shout that creates fire. Interesting. I like how the dragon shouts are really just shouting words.
Yes, it was there since the beginning.
It wasn't there from the beginning. The only thing that was there before was the sound it makes when you scroll over Alduin being sealed and the sound of wind in a cave in the background. It didn't used to have the drumming or the other sounds, I know because I looked over the wall when the trailer first came out because I was ecstatic that they finally announced the game meaning that it wasn't long before they showed me the game.