If I recall correctly, that is a kerning issue with the font. At the edges of the font is not a solid line, but rather more like every other pixel so that the characters can be closer together. This causes the up/down movement of one character to the next, as they fit together like poorly made puzzle pieces. And just how bad it looks depends on the size of the pixel on the monitor, and how much "bleed" it has with it's neighbors. (I don't recall the tech terms for this.)