Interesting Issue with Sanyo Hybrid Bike

My Sanyo Hybrid Bike's front wheel vibrates every time I free-wheel. I called the Agent and the technician came over to replace the front wheel. The new front wheel vibrate less but still vibrates. All my other bikes do not have this problem. Maybe the motor/dynamo is the root cause. Anyway, I will test ride tomorrow to see if the fix works. The wheel is okay when peddling or charging back during braking. The moment it free-wheel, the vibration starts and it get not only noisy, it also uncomfortable as the vibrations transmit to the saddle and my butt gets all the woozy. I hope it is do not vibrate as much with the new front wheel.