The noise is different between to the two cameras. The K7 is much maligned about its noise, but its really not that horrible. I took some comparison shots when I first got it. Like Scott, I noticed that the K7 has better control of color noise - the K20 has a fair amount of magenta noise, especially in the deep shadows that's really distracting and sometimes harder to deal with. The K7 has more luminance noise at mid-tones but less color noise in the dark shadows. So I wouldn't call the K7 worse (or better), just different. Not hugely different, but there is differences. I do not think it is as bad as many would have you believe in some of the posts I've read elsewhere.
On the other hand, it's no match to the Kx. And it looks like the K5 is going to be much better as well.