crackle on old receiver from pc in surround mode

[gomjabar]

I run my htpc sound from the analog out of my sound card to an old receiver that only has RCA inputs. When I use 2 speakers or headphones and either surround sound or theater mode (both use center channel) I get a wierd electronic crackle. The only reason this is a problem is that I want the better sound of a 3 channel setup and still use the headphones when I workout. Any idea how I can set this up?

 

[gomjabar]

I should add that this doesnt happen if I run the sound from a DVD player. Then I can use both 3 channel and the headphones.

 

[gomjabar]

ok tried a different sound card but got same results. The crack is seems to be the audio channel as it only happens when someone is talking. Also some recorded sources do it and some dont. Im guessing that the stereo sources are doing it and the 5.1 and higher are not.