Ok here's the deal.... I bought this great Vizio LCD TV and had Comcast come over and hook up the box and install the cables. The TV did not come with HDMI cables so I bought them. Here's the problem: When I change stations between hi-def and regular broadcast there is an annoying crackling noise, like static, or a buzz. Only from hi-def to regular or regular to hi-def. It doesn't do it with the regular RCA cables. What do you think the problem is???