Grainy discolored textures

[halo]

My lightmaps are completely gray scale, stored as RGB 24-bit, and rendered with no lighting. Every pixel in the texture is a grayscale shade, but I am seeing grainy splotches of red and green when rendering. I am using GL_LINEAR for the mag filter, which is what is used at the distance in the image below. I am not using texture compression in this shot. I increased the screenshot's saturation so the problem would be more easily visible.

http://www.leadwerks.com/post/test.jpg

You can see in this shot that the pixels are horrendous. This is a smooth-blended grayscale image, and it is getting displayed with what looks like severe compression artifacts:

http://www.leadwerks.com/post/lights5.jpg

[halo]

Interestingly, I looked at the settings on my GEForce 4 MX, and found that the "image quality" was set on "performance" quality. I changed the setting, and everything is fine now. There must be some internal compression method the card uses.