there's the same bug in Trackmania² - Canyon like in the Assassin's Creed games from the first to the game 'revelations'.
I don't know, maybe you're using the same soundengine, I don't know, but when you use your 5.1 or 7.1 Soundsystem and you're configurate the setting at windows to 5.1 you won't hear any carengine sounds. Just the music and drifting.
Maybe Nadeo is able to ask the developer of AC III how they fixed it
Regards
Lowfry