Need Help w/ Apple TV Audio

Okay so I'm setting up an Apple TV and having issues with the audio. I've got it hooked up via HDMI and when I'm scrolling around the menu I can hear the little clicks of the menu so I know the audio is working. Then when I run iTunes I can have the audio play out of the TV. However the only time I cannot get the audio out of the TV if I'm mirroring. I can see my desktop and the visual part of the mirroring works okay, however no sound from the TV.

Issue is I can go to System Preferences and chose Audio Output, I can see Apple TV it just won't let me select it. When I click Apple TV, it deselects?! Very frustrating, any help would be great!

I restarted everything but the computer, yeah I'll try that tomorrow.

So the issue was I was plugged into an ARC HDMI port. I didn't even know there was more than one time of HDMI port. I switched to a normal port, and was good to go!

http://hdguru.com/what-is-hdmi-arc-and-what-does-it-do-for-your-hdtv/