I notice this myself when I do ribbing as well. It's because (I think, at least
) people usually knit at a slightly different tension than they purl, and when you switch from the knit to the purl it can create a bit of a "gap".
In my case, it's not permanent ... I'll notice this "laddering" effect in the first few rows below my needles, but rows below that are fine. I think that it is such a small gap that the stitches eventually even out as you get farther along. It has never been noticeable in any of my finished projects, so I don't really see it as a negative or something that I need to fix.
If you're only a few rows in, I would suggest toughing it out for a couple of inches and see what you think at that point .... some stitches (especially ribbing in my experience) need at least an inch or so before they really start to look good.
If it's still a problem at that point, then you may need to work that first purl stitch a little tighter.