Sound Problem, Please help

I have my Xbox connected to my stereo through the advanced AV pack via an Optical cord. When I play games in digital dolby the sound crackles at high pitch, even when the volume is low. When I turn off the digital dolby the sound is O.K.

Is this a problem with my stereo, cable or xbox???

Also the digital dolby and dts works fine when playing dvd movies, no crackles to be heard....

Thanks

Maybe there is an input volume on your Hi-Fi you could turn down whilst playing the XBOX?

Or you may have to just adjust the sound settings in the options screen for each individual game! :(