First, make sure you've got the sound folder for the ISI BMW F1 car in that install, in case you used a rFLite install. That folder, named FBMW Engine, goes in the Sound folder. If you're using a full rF install, disregard.
Then, put the .sfx file that Darren made in Vehicles/IndyCarSeries/2009 Season folder, replacing the old Indy.sfx file. Be sure and back that one up in case you want to replace the addon one later.
"Sometimes I wonder whether the world is being run by smart people who are putting us on, or by imbeciles who really mean it.
"Politicians are like dirty diapers. They need to be changed often and for the same reason.
"I do not suffer from insanity. I enjoy every, single minute of it."