From ReadMe: "GTR Evo is needed for sounds, or the .aud file could be replaced with another one."
You can copy an .aud file from a car you have installed and then rename it and replace 'TTA.aud' in ...race07\Gamedata\Teams\STCC_2015
As you can see the mod works for most people here. For some reason(s) the game can still ctd for a few persons, but to downrate is not a good way to report a problem.
You can copy an .aud file from a car you have installed and then rename it and replace 'TTA.aud' in ...race07\Gamedata\Teams\STCC_2015