I played your file in both VLC Player and on the timeline in Nero Video. As far as I can tell, the transition area you're talking about is at 25 minutes 7 seconds. I don't hear the sound of the water continuing at that juncture. I burned it to disc and the result is the same. You can edit the audio of a video track in Nero Video. Sometimes, WaveEditor is necessary, depending on what you're trying to do.
Yes it was always fine when an mp4 such as i sent to you, was only after burning i had the issue. Seems ok now though.