Turbo requires samples. Samples are basically wav files, recordings of parts of the games audio. They're used when it's too difficult to emulate the analog circuits used to make sounds in certain early games. The entire set of samples for turbo is about 9 files totaling about 637KB. The file is called turbo.zip and should be in a folder called samples. If you don't have anything in your samples folder, you will need to go out and find Turbo's samples file.
If you have a turbo.zip in your samples file already, check that you have samples enabled in the settings.
The file should have:
01.wav
02.wav
03.wav
04.wav
05.wav
06.wav
ambulance.wav
idle.wav
skidding.wav