If you travelled at a great speed toward a noise source, you'd hear higher and higher frequencies, at a great enough speed the pitch becomes infinite; basically you hear the entire noise in an instant.
If you travelled at the speed of sound away from a noise source, you'd be travelling along with the waves of rarefaction/compactification and would hear nothing. The pitch would be reduced to zero.
If you travelled above the speed of sound away from the noise source, then you'd hear the noise reversed in time. Basically, negative pitch. The last thing you'd hear would be the temporal beginning of the noise.
No idea what the game does exactly though