I've noticed it. I thought it was my TV, but FOX was showing the same program and when I switched over the crowd noise was so much louder.
I sent them an email and told them their BIAS was showing.
When the president was at the G8 conference, I sent them an email and said:
"Do you think it would cause C-Span too much pain, to show America our President's meetings, speeches, etc., during the next fews days, while he's across the big pond? I'm not talking about the protest, either. While I realize you'd rather show that, America is interested in the President, not the trouble makers."
Lot of good it did. I don't remember them showing any of it. I could be wrong---have been before. :)