Your old JVC may also have recorded your audio in a different way so that a more upto date camcorder may have problems playing it back. It may have something to do with the speed at which the video tape was passing under the record head(s) or it may be down to a different codec used. In the video part of Mini DV a codec called Microsoft DV AVI II is used so the same could be applied to the audio part and the one of the JVC may have been different to the one on your new Canon, it's just a thought.

__________________
Better than a poke in the eye with a pointy stick any day...