I have this HDTV ready Panasonic rear projection TV(51 inch) I get great picture for HDTV and DVD. I have noticed this shadow line that moves from the bottom to the top. I thought it was my connection for the satalite Box or dvd player, but I can see this shadow moving on input that do not have pictures or when I turn off the satalite. It does not disrupt the picture, except for the slight change of shadow moving . Is this a sign of a dirty projection mirror or is it a common feature. my tv is 4 years old. Is it worth a visit form circuit city to Fix? please advise.