When using the "modded sounds", default cars / up to date modded cars will have no sound. Its a fix for older car mods which have broken sounds and lets you quickly swap between the two.
Nice idea, however I don't understand how this app works. Where do the modded sounds come from? If I use it now, there are no modded sounds and there is no sound at all. Switching back to the original sounds works okay.
It simply replaces the default sounds with the "ac sound fix for 1.4" which allows certain vehicles which have no sound (or exterior sound) to work again, however using this fix causes the default cars to lose all sound completely. This app simply provides a convenient way to swap between the two (Sound fix and default) depending on what you would like to drive.