I've had a vibration with mine since I bought it with 8 miles on it, has about 6,000 on it now. Road force balanced tires 2 times, didn't really help. WELL! One of our techs found this today, and we checked another one with a vibration, and sure enough, same thing. Something with the left rear axle/face on the axle is out of round. I put a magnetic screw driver on the e-brake shoe as a reference. Watch the gap between the axle face and the screwdriver.