Help with horizontal lines ruining my hd picture

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Have a samsung 42 inch plasma with a sony strdg 510 reciever. Running the video via component cables through the reciever. So the component cable is going from the motorola hdtv cable box to video in on the reciever and then from monitor out to the back of the plasma. Everything is hooked up correctly I've checked many times! However, on the hdtv channels only,I am getting purple horizontal lines which start at the bottom of the screen and slowly progress up. One after another. Very frustrating to say the least. Besides these lines the picture looks great. Remember I don't see them on the regular sd channels.
Things i've tried: bought better component cables, separated the plug in cables from the component cables as to decrease interference. Lastly, the cable cord coming in from the wall is good rg 6 coax with good ends on them.
Is there something wrong, what is the answer. Also the motorola hd box is bran new and so is the reciever and plasma. Can anyone help...
Thanks Astonn,

What happens if you bypass the receiver?

However, on the hdtv channels only,I am getting purple horizontal lines which start at the bottom of the screen and slowly progress up. One after another. Very frustrating to say the least.
You have the classic symptoms of a ground loop problem. Getting better cables is not going to help. Ground loop occurs when something is at a different ground than the rest of the equipment. Odds are that the co-axial cable line is not properly grounded. Are the TV, receiver, cable STB all plugged into the same surge protector or power strip?

If you have a DVR, disconnect the co-axial cable line from the STB and see if the horizontal bands are still there on playback. If they are gone, then the cable line needs to be properly grounded. One temporary fix that might work, if you have a surge protector with RF input/output connectors, is to run the cable line through those RF connectors. This may ground the cable line to the same ground as everything else. The proper long term fix for a poorly or ungrounded cable line, is to fix the ground at the cable box going into the house or building. You may have to get a service call from the cable company. But confirm that the problem is with the cable line first.

What happens if you bypass the receiver?

When I bypass the reciever they are still thier, but seem to be fainter.

You have the classic symptoms of a ground loop problem. Getting better cables is not going to help. Ground loop occurs when something is at a different ground than the rest of the equipment. Odds are that the co-axial cable line is not properly grounded. Are the TV, receiver, cable STB all plugged into the same surge protector or power strip?

If you have a DVR, disconnect the co-axial cable line from the STB and see if the horizontal bands are still there on playback. If they are gone, then the cable line needs to be properly grounded. One temporary fix that might work, if you have a surge protector with RF input/output connectors, is to run the cable line through those RF connectors. This may ground the cable line to the same ground as everything else. The proper long term fix for a poorly or ungrounded cable line, is to fix the ground at the cable box going into the house or building. You may have to get a service call from the cable company. But confirm that the problem is with the cable line first.

The plasma is plugged into its own outlet and so is the stb. I'm assuming you mean set top box or hd cable box. But the reciever and dvd player are plugged into a surge protector power strip. When I disconnect the coax from the hd motorola box, not a dvr by the way, the picture freezes without the lines. Therefore, you are problably right, I will be calling the cable company to have them take a look at the grounding situation. I don't have a surge protector with RF connectors but thanks for the idea. if the cable company will be awhile I Just might pick one up.
Thanks,