These are the game sound effects. Those ending with "_lp.wav" are looping sound effects (like engines rumbling) and should not be compressed to mp3 unless you have the technical know how to make them tesselate properly on decompression. The mp3 effects are single-shot effects. However, you need to decompress them to wav files before they can be used in the game. Make a note of the looping wav file format when doing so. That's the format you want to use, either 16-bit mono or 16-bit stereo. There are a lot of wonky variations of the wav format out there, so if it doesn't work, try saving in a different wav format (or add support in i4 for every wav format variation :).

You should install an mp3 player as a helper to your web browser if clicking on these links prints out garbage.