There are a few things that can cause this:
1. A DC offset or difference between the beginning of the sound and the end. Using an audio editing program, verify you don't have a DC difference between the beginning and end, by zooming in on those sections. If you do, you can adjust the amplitude to fix the problem. Then save it out as listed below.
2. Part of the file's WAV header is being interpreted as audio data. Save the files as Windows PCM (*.wav) audio 16bit stereo 44.1KHz. Uncheck any checkbox that says 'save extra non-audio information'. The Audio Machine expects a certain format of the Windows WAV Header, so this will format it correctly, leaving all the extra non-audio data out of the file.
3.