It is debated if the brachiosaurus were warm or cold blooded animals. This is because if the brachiosaurus was warm blooded, it would require around 400 pounds of food a day to sustain its mass. This is a very large amount of food considering the brachiosaurs main diet was very high vegetation. If it were cold blooded, it would take substantially less food per day, but it would take 100 years to reach full potential.
This section of the site includes many interpretations on what dinosaurs may have sounded like. Note that these are just interpretations but it's still fun to listen to. 
Below is the Gallimimus' roar (in .wav format).