It isn't obvious, but if you go though the same menus that you go thought to change balance/fader/bass/treble, you will find it. It isn't labeled anything as obvious as "disable RDS", it is more like a display option, where you can select to display the frequency instead.
I wish I could be more specific, but I ain't in my car at the moment. If you still have trouble finding it, I'll look again and take notes.
This is also where a nifty feature to have the car automatically adjust the volume depending on ambient noise. I didn't know what it was at first, and saw that it was set to "low" by default. I set it to high, and was blown out of my seat when I gunned it in a merge lane.