What things cause bars of out-of-sync pixels across the picture?

I've been getting narrow bars of what look like out-of-sync pixels completely across the screen on some recordings -- haven't noticed on live TV, but don't watch much of that. It doesn't happen on all recordings, and it happens on more than one channel. In order to trouble-shoot, I need to know what can be causing this and what the most likely culprits are.

I figure it could be:
Comcast cable
InfiniTV tuner card
WD hard drive, Caviar blue 500G

What about the graphics card? AMD Radeon HD 6450

What else could cause this?

Which is/are the most likely, and I will try to tackle that first.

Thank you in advance.

Mostly, this is caused by signal issues. I've experienced this, and found that when viewing the same recording on an extender, the distorted area of the screen is much smaller. It appears that the graphics card in the PC doesn't handle errors in the video very well, and causes a horizontal band of bad blocks all the way across the screen. I've tested both the Radeon HD 6450, and the nVidia GT-430. Each has a bar all the way across the screen at the point where the video errors are in the recording, but they look a little different on each graphics card.

The solution is to work on your signal strength and quality. In the InfiniTV's web pages, you can check signal strength and quality (aka S/N or SNR). Both can vary from one channel to another. You'll usually notice that lower-frequency channels are higher strength than the higher-frequency channels, so you have to balance them out.

You want your signal strength between +/- 10dB (closer to zero is better), and your Signal to Noise Ratio (S/N or SNR) should be 35dB or higher. There is a tool that you can use to automatically test low, medium, and high frequency channels on the InfiniTV. It can be found at the link below:

Windows Experts Community

Thank you for the information, barnabas1969. I will work on those points and see what I can improve.

You're welcome. If you need more help, there is a large community of Media Center users at TheGreenButton. If you post there, you'll have a much larger audience of experienced Media Center users.