We're excited to announce that we've fully migrated the Xbox Forums to their new home, here on the Microsoft Community forums!
As of today, going to forums.xbox.com will redirect you here to the Xbox area of the Community forums. We've moved all of your existing threads over so you can continue and start conversations with the new forums experience.
We sincerely appreciate the feedback you have provided over this transition and can't wait for you to check out the new Xbox Forums!
Thanks for the replies, I found out why this happened although I still don't know why. My 360 decided to enable discovery in the display section of the settings and this changes the hdmi audio output for some reason. It managed to do this overnight whist
switched off and unplugged, LOL. Shows the fix here.