By nick, fo you mean a scratch or a crack, or a small loss of metal at the edge, probably from being banged? Regardless, unless its an actual crack there's no need to do any thing. It sounds like you may want to clean them up for cosmetic reasons. There is no filler that you can use and sanding or buffing to remove the nicks would be highly inadvisable. You could permanently alter the sound and the end result might be more visible than the nicks.