if you over tightened the cones, you could've damaged the race or cone. if you take a pencil and run it along the race and cones where the bearing ride you can feel any pits that you may not be seeing with your eye. or you might've flatted some bearings. did you rebuild this with new bearings? cheap hubs have cheap bearings. if your cones and races are ok, try upgrading to high quality grade 25 chromium bearings.