You can edit the files in a WAV editor. If you don't have one, a nice free editor is Audacity (
http://audacity.sourceforge.net/).
If it's clicking when you loop a sound, the click might not be
in the sound, but as the loop switches from end to start again. Try and make all your edits on a zero-crossing point (where the level goes from + to -). Beware that this might not work first time, you may have to try different loop points, and only experience will make it easier to get right...