Re: Sony Bravia audio issue
It's alternate digital audio; the content depends on the channel. For some channels it's Spanish, for some channels (notably PBS) it's additional narration - descriptions of what's happening visually (I assume this is for visually-impaired people).
There is a Sound menu option for non-digital channels called "Alt. Audio/MTS" in which you can select "Auto SAP", which will automatically switch the TV to second audio programs when a signal is received. However, I do not see such a choice for digital channels. I do not have "Auto SAP" selected for any analog channels, in case that makes a difference.