Havent use the bike for about a week due to dead battery, now the battery is ok and running smoothly but at slow speeds to 5 to 20kmh, as i release the clutch a clanking sound coming from just under the engine, sounds like a loose metal thing inside a shaker (like bartenders use to mix drinks). do i need to worry about this? when going to more than 20kmh speeds the clanking disappears though......