This is most commonly encountered with Google Maps and Satellite mode, but can also happen with regular maps and an urban area with densely packed roads. When Maps has to render lots of video data, or quickly zoom in and out, any audio stream will begin to bugger and lag. The only way to get caught up is to enter a situation where video no longer needs to update as frequently, such as stopping the vehicle or moving away from Maps, and then providing enough time for audio to catch up.
It almost feels like there isn't enough bandwidth over USB to provide all of the data.