Why does my finished drywall look like it has ripples in it after painted?

I pulled a few pieces of drywall due to a mold problem and replaced it with mold resistant sheetrock. I finished mudding and sanding the repaired areas last night and threw a couple of coats of paint on it. It looked pretty good when I was finished. This morning when I woke up I looked over and noticed the patched drywall has horizontal ripples all the way down in the sunlight! There are even ripples where there is no mud! ARGH! The only area that is not rippled is the outside corner where there is a lot of mud. I have done a little drywalling in the past, and have never experienced a problem like this before. What has caused this, and what can i do to repair it? Thanks in advance to anyone who answers, and I will choose a best answer!