They may be more costly on your hard drive space, but you'll really want to use WAV files over Mp3. Mp3 is a lossy format, meaning the data is compressed then decrompressed leaving a representation of what the audio is supposed to sound like rather than what the audio ACTUALLY sounds like. At higher volumes, you'll notice a difference (and don't you want that s hit loud?!).
What program are you recording into?
Cuts, pastes, and builds something.
