@Dugath:
1. When you say it doesn't happen live, do you mean on the same show?
2. Is it actually at "scene" changes, or when going to commercial and/or coming back from commercial? If it's at commercials, then, as mentioned by @RogersMoin, it may be your sound system having difficulty switching between DD5.1 and DD2.0 input signals (one audio format for commercials, one for programming). This means there's an issue with the audio system. The way around this would be to send only one format to your audio system. Go to Settings - Audio - Other, instead of DD on the NB3. Another option would be to perhaps change the audio decoding method in the audio system. Many less-expensive audio systems like sound bars and HTiB systems have these sorts of issues with incoming audio format changes.
3. If this is happening when connected directly to a TV, then I have no suggestions - perhaps someone else.