Get the "PAC Manager", open common.pac (under data\sound) and then sound #8
You can make your own wav sound, just don't exceed the size of the original file.
I think you can just replace it with the "normal" step sounds, which are a few sounds before the Racast one.
racast is of my favorite pso chars, the only annoy me too much is that step sound, it would be nice to be fixed directly from the official ephinea server than to become personal intervention which will not passed to all users.
I don't really think it should be fixed (because nothing is broken) and pushed to people who don't want/need it.
After all the change is not that hard to make yourself just like I suggested to Spuz.
I had made a kinda more annoying one with a squeaky sound (wasn't my idea), but it was actually funny.
Here is the file with sound 4 copied onto sound 8 (4 = some normal step sound, 8 = garbage truck) Download Here