Hello Manuel,
the sounds for e.g. riding over the curbs are defined by the material settings of the curbs in relation to the *.tdf entry of a track.
You can find its definition in the Rumble Strips section of the *.tdf file.
The default is "rumble" and the soundfile can be found in the ..\GameData\Sounds\Secondary folder.
If you want to have other sounds for your mod, i would suggest to create a new soundfolder-structure for it and set its path in the *.rfm file.
Copy and paste all "default" sounds folders, like "Default", "Ambient", "TMTires", "Secondary"... and the soundfolder of your car(s) into it then.
Now you can replace the default ones with own soundfiles without changing it for the whole game/other mods.