I cant help much because I'm not at my LFS machine and have no files to look at. But iirc there is a BOV/Dumpvalve made by yamakawa thats sounds alot like the sample you posted. Its really loud and screechy. Its the last one Boost5.wav or something like that - it might be number 4, I can't remember. (He made two sets of 5 Boost samples)
Have a look in the [Sound] or [SoundLibrary] folders inside the [CSR] folder. You should be able to find it there.
Make sure CSR is closed when you do this. Copy that (BOV) file to the appropriate [USER FILE] >> [car] folder. (XRT for you) and replace the original BOV file with the newer (louder) one. You will have to rename it so that CSR can find it in the XRT folder. Look at the naming scheme in the XRT folder. It should be named XRT_boost.wav or XRT_bov.wav - I cant remember at this point.
Hope you can figure all that out.
