"Glitchy" lines on laptop

Help! I'm lazy! Not really, I just don't want to ship off my computer for repairs if I'm wrong about this. As the title says, I occasionally have these blinky, glitchy lines on my laptop screen. The thing is, it doesn't happen when I turn on the machine or when I restart it; only after a few or several (2 to 24) Hours.
EDIT: The lines tend to appear along the top of the screen, and seem to spread from just below the top right corner to the top left in a perfectly horizontal line. Said line blinks in a random rhythm, occasionally with some further down and originating from the left. I notice it most often after browsing the internet for awhile using firefox.

Is this likely a hardware issue, or have I stumbled on a wonderful new form of glitch in Windows 7. I don't really know what specs are necessary other than it's a Gateway, almost two years old and tends to be on (and plugged in) more than it's not.

Check your screen's refresh rate.

Only option is 60Hz. I should perhaps clarify the appearance of the lines. I'll edit the OP to include.

Sounds like a hardware issue, most likely the video card overheating or kicking the bucket, can you gauge the temperature of your hardware after a few hours of use? How old is the laptop? What are your specs?

The laptop is nearing two years old I believe. It's a Gateway NV55S, AMD A8-3500M APU processor, 6GB RAM, AMD Radeon HD 6620G Integrated Video.

I wouldn't say it gets hot, at least not compared to the first laptop I had. (A Dell that could melt a Hershey bar in under 30sec) I always have a cooling fan sitting under it and it's kept in a cool room most of the time.

I do have an extended warranty on the laptop, so I could get it fixed; or quite likely reimbursed. Would it be worth sending it in with a "broken" screen and upgrading? Or should I let them fix it and just pay full price for another later?

If its under an extended warranty would say just send it in i mean you payed for it so get some use out of it. Could open it up if your comfortable with the idea and clean it out/check screen connection( Opening it may void your warranty so read it before doing so. )

I had a monitor do this when I tried to plug it in via DVI. No matter what comp I used the DVI connection would give me green lines that would increase over time as the monitor warmed up. However if I switched to VGA the problem went away.

Check the monitor out.

*sigh* I guess I'll have to call it in on my next day off, seeing as I'll have to go by an Office Depot and get the number. Thanks guys.

Can it be that your monitor is "Garbaged"?
If that's the case, either the *thin* connection to the screen lost its integrity or the LCD screen itself is broken.

... or your laptop is an Acer.

EDIT: yep your laptop is an Acer.

(Seriously, it's a hardware issue)

Yeah, I just have to ask: If it's only intermittent, how can we be certain it's hardware? As I said above, it tends to happen most often when I leave Firefox displayed. I'm just curious. (And a lazy ass about raising a ruckus that concerns me in any way.)