Hi!

I bought and downloaded the "Knife on Dunwall" DLC through Xbox Live marketplace, and have a major sound problem.
All DLC-specific sounds are missing in game. Standard guard speeches and sound effects that came with the main Dishonored game seem to be present, but there is no sound in all dialogues, and even no subtitles for them.

I tried changing locale, re-downloading the DLC and clearing cache, but all that made no effect.
Please suggest a fix, because that makes the game unplayable.

When you tried re-downloading the DLC, did you delete the DLC content from your hard drive?

Yes, of course.
I re-downloaded the full DLC.

If you continue to experience issues, I would recommend contacting technical support. Information can be found on the back page of the game manual.