Moving line through plasma and LCD TV's

Question

3 wall mounted TV's one Plasma and two LCD's all linked together. all TV's have a faint horizontal line that slowly moves from the bottom of the screen to the top and continues to cycle through. When cable is disconnected and DVD player hooked up picture is perfect. Have changed out the cable box and checked the cable signal strength(good)as well as stretched out new coax cable to the TV's and the problem does not go away. Any ideas?