Does thids happen with specific cars? If so, which? I'll take a look into my 'Bude install.
Usually when this happens, it's because there's an add on soundpack and there's be say in the GT350's case a file called shelbysounds.aud in the car's folder which you remove and it works with default sound. But I don't recall the Altbierbude using the soundpacks though someone may have uploaded a car and not removed the aud file THEY (the skinner) were using.
Do the default caras still work?
And you say 2 cars? Did you do the updater install? Or did you just add a few skins? My original answer at top is based on using the updater so full 'Bude install.