I'm getting a pop noise out of my speakers when I first play a piece or media or when I skip forward/back. This happens only over Optical, and when I use HDMI it isn't there. For my current setup, it isn't possible for me to use HDMI, so I've got to go Optical. Is this popping due to my computer, receiver or optical cable? If I had to guess I'd say it's the optical cable or computer... Any help eliminating this annoyance?