It's my understanding that you can get some popping when switching from SD to HD. I get it sometimes if I flip back and forth from one of my HD channels in the 900's to say 57. As the picture re-syncs I'll get some popping sometimes. Sometimes the dropouts don't go away and I have to turn everything off than back on again. I'm told this is "normal" but whatever. It's annoying when it happens. On my setup, it's likely an HDMI handshake issue.