@Amandab6
If you have a newer Ultra (4800/4802/4850) make sure of the following settings:
1) Configure passthrough: Settings/Audio/Digital output format = Passthrough (do NOT use Auto, as that can cause the issues you describe due to transcoding)
2) Disable Sound Modes: During playback of any video - press Options (*)/Sound settings/Customize sound modes/Volume leveling & Dialog enhancement = Off