Select the XRT and leave pits.
Hit CTRL+A. When the car sound options come up, select Load and then from the sound list select XRT_defualt (or something like that, recalling from memory, I can't recall what's it called).
IF you are already using XRT default (having previously over-ridden the default XRT with the XRR sound), you might have to get the default XRT sound and place it in the relevant folder. If this is the case, let us know and someone will post the default XRT sound file.