MacBook pro display lines

Hi,

I've been noticing lately (the past year or so) on my MacBook pro display that there are frequently horizontal grey lines going across my screen. I've noticed it mostly when the display color should be grey or white, but that's not always the case. It occurs mostly in my Google search bar using Firefox, and also occurs heavily on Facebook in the comments/reply section of a post. Outside of the browser I've also seen it when looking through some personal photos, especially of the sky, the lines will seem to sort of outline different contrasts in white or light tones, kind of like the Magic Wand tool would do in Photoshop. The lines do flicker and change when scrolling.

This may not have made any sense but it's the best I could describe it. I attempted to snap a photo with my iPhone the best I could.

My specs:

13" Macbook Pro (2009)

Intel Core 2 Duo 2.26 GHz

NVIDIA GeForce 9400M

Resolution: 1280x800, 32-bit Color

Any ideas? Thanks in advance.