I have a Nvidia 130M graphics card, on an Acer Aspire 5739G model laptop.
When I play games, any games, every few seconds there is somewhat of a "scan line" tear that's horizontal and runs from the bottom of my monitor to the top and slightly shifts the pixels on the screen to the position from one frame to the next. It takes about 2 seconds for the line to go the height of the monitor.
It's not very noticeable, but a tear type of "line" is visible as it goes up the monitor.
If I'm moving the screen a lot, causing a lot of pixel color changes all around the monitor, they become extremely apparent.
I've also noticed that there's a 1px "scan line" horizontally across the monitor consistantly in a position about 1/3 down from the top of the monitor. There's also a vertical "scan line" roughly in the middle of the laptop too.
This is only visible in full-screen DirectX applications, with one exception: A flash game I enjoy, Everybody Edits, also has this problem, and I see the horizontal "scan lines" going up the flash application (not the entire monitor).
The reason I keep quoting "scan lines" is because they're not true scan lines, nor are they even lines - what it really is, is there is a 1px line where all the pixels are shifted to the left by 1 pixel, which is only slightly noticeable unless you're in a place with a huge amount of color differences.
It's a tearing effect, the foreground doesn't update the same frame as the background, so there tends to be little lines or "tears" across the screen where an update is taking place.
What could be the cause? It's not a huge issue, but it is slightly noticeable and I would love to know why this is happening.