It seems the editing software you're using doesn't like the audio compression used by your camera. Annoying, huh?
Additionally, MPEG itself isn't the greatest medium for editing due to the way in which it's encoded. So, you can do one of tow things:
a) re-encode the video to DV (an editable format supported by all editing software); or
b) buy an editing application with MPEG editing support such as MPEG video wizard.
http://www.womble.com/download.htm
DVD camcorders aren't the greatest for video editing, but there are workarounds.