I would do one of two things.
Send the 360 in and have it repaired. (I assume you have swapped HDMI cables) If you purchased it new, it's under warranty. If not, I'm a dealer and can hook you up with an Arcam authorized repair center.
Run your video to your T.V or PJ and run the audio only to the 360. I'm actually using a 360 at the moment while my amp gets checked out and this is the way I'm using it.
Send the 360 in and have it repaired. (I assume you have swapped HDMI cables) If you purchased it new, it's under warranty. If not, I'm a dealer and can hook you up with an Arcam authorized repair center.
Run your video to your T.V or PJ and run the audio only to the 360. I'm actually using a 360 at the moment while my amp gets checked out and this is the way I'm using it.