You can use a very fine whetstone, and rub a wet coin lightly in a figure of 8. You have to be careful because half dollars (unless they are pure silver) are silver plated. So if you rub to much you can take away some of the silver finish and reveal the base metal. I use this technique on all my new coins when I buy them. If you do it carefully you can soften them enough to take away most of the 'noise' (im assuming thats why you want to soften them).