Dolby Digital / DTS Audio, hiss / chirp at the start of Movies

Is there something other then turning both these features on that you need to do for both to pass through audio from an Apple TV -> TV -> receiver? If I have these options enabled, files with those audio formats play a hiss / chirp when they start to play then the audio goes to 2ch.

In the main AppleTV settings (Audio / Video) I have it set to auto, and in Media Player both are set to enabled. My Apple TV is connected to my TV via HDMI, and my TV is connected to my receiver via an optical cable. I know my TV can do pass through because it works with my PS3 (HDMI to TV) and it worked on my WDTV Live (HDMI to TV) that I had before I replaced it with an Apple TV.

I inadvertently had my receiver set to Matrix (emulates 5.1 from a 2ch source) so I didn’t realize it was like this until recently. I’m running iOS 5.01 and ATVFlash 1.6.

Any ideas on what I’m doing wrong?