When the ball is rolling, play a roll sound cue (looping), increasing it’s pitch if it’s velocity increases.
On tick, check the previous and currect Z velocity. If there is a big change, that’s your fall. You can do that with a hit event on the ball if you desire to play the same sound on land or if it hits something.
Here is a relevant example of pitch going up with velocity: Turbo , Engine and Nitrous Sound Setup - YouTube