Use a rasp or machinist file to get the ripples out. Run it the length of the limb, keeping it as close to parallel as you can to the limb. This will knock the high spots off while leaving the dips untouched.
I use a rasp early on in the tillering process, and then switch to a file later on to avoid making deep scratches in the wood. I do this often in between scraping sessions, because sometimes the scraper itself induces a bit of "washboard" into the belly wood.