This is going to reveal my advanced age grouping , in the "olden days" we used to fill our motorcycle handle bars with sand to reduce vibration especially on big singles and twins that sent a buzzing vibration to your hands and wrists, just got river sand (not salty beach sand ) heated it up to dry it out completely and slowly poured it with a funnel into the end of the bar that was held upright with the other end plugged ,hard to believe but it works a treat, cheap fix .