A quick update to share here.
To turn this functionality on or off now requires a fast double-press of the *(asterisk) Roku remote key, in order to turn on or off. This must be done on either the Netflix home screen showing the categories of content, or on the content details page of any title.
I have a Roku Express, and had the non stop dialog box in the top left of the screen when watching Netflix. Couldn't get rid of it until -
1. While watching your show, exit out
2. Return to main netflix menu
3. Click the * button 3 times quickly
4. You should now hear "audio _________________ diasbled"
5. Go back into your show, and enjoy