@thehiredgun
They can also be .ogg files or mp3s', however
some types of mp3s' don't work ,
mpeg type comes to mind. Check by right-clicking and viewing properties, sounds like you may have those.
You may want to get an audio converter, lot's of free ones on the internet.
@Archie,
Welcome to subsim
, from what I understand, .wav are probably one of the more stable formats, however I have used mp3s' as well.
RDP