I've gotten a head-wobble when riding on interstates above 60 mph and there is turbulance from traffic moving < 150 feet ahead of me, or during weather-related buffeting. It is a continuous rapid shaking where the bar-ends move about 3/8" to and fro. Tire pressure is normal. I've ridden above 70 mph on isolated roads and the bike was fine. Anyone experience and correct this?