Speedo/tach makes a buzzing noise when accelerating....comes and goes and it is loud like gears turning...quiets down at cruising speed, so maybe it is the tach. I took the speedo apart and oiled the odometer gears, (only gears I could see) but that was no help. Now I put everything back together and my tach now idles at 400 instead of its usual 650. Is there a way to recalibrate the tach and what do I do to stop the buzzing sound?