I seem to be having the same problem as another user: "TV connected to AppleTV makes horrible noise on startup and when waking up from standby"
In my case, I'm using a stereo receiver for audio playback (instead of a TV). I'm using the optical audio out, but it goes through an analog converter and goes into my receiver as stereo RCA.
The horrible static noise starts when I turn on the apple TV and receiver. The noise disappears as soon as I press play on my iphone or itunes. The static doesn't come back when I press pause - it only occurs from the time that apple TV starts up until I press play. Hmmmmmm....