Yeah, i was wondering this too...
Looking at the Trailer, it seems they are re-using the original Rollcage vehicle sounds, which is awesome, but the 'Homing Rocket' and 'Machine Gun' seem to have welcomed updated sounds.
What is also new, is the 'Turbo Boost' sound and obtaining a hologram pickup sound, but with these two i miss the old Rollcage sounds. I'm not sure if 'Turbo Boost' has a FX sound upon use. I think i hear something subtle amidst the vehicle noises.
I wonder what sound FX they can re-use without copyright issues, and which ones they don't want to re-use to can't re-use.