XGRA: Extreme-G Racing Association Hints for PlayStation 2
Also on: XBox
Enter 'FREEPLAY' as your name to get all racing levels...
To break the sound barrier just go onto Siris Canyon and once you reach around the end of the loop use your boost (best to have 400 G engine) and wait.
The sound will disapear and then come back!!!!!!!
Also on: XBox, check out those pages for more help with this game.