Whenever you hear a sound coming from your bike, stop and take a moment to evaluate it.
Most of the vibrating sounds can be fixed by tightening up spokes and other items.
Now if after an inspection you hear a clear buzzing coming from your motor it might be because of a loading issue. This can happen if:
-Your tires are too low on pressure
-You have the bike at loading limit
-Your battery level is too low
-Your assist level is too high for a low battery level
-You are going up a hill with throttle only
-You are trying to start moving from the stop position with throttle only while any of the above items
Note: It is NOT recommended to overload the motor while going on a steep hill. This will wear down your controller and could damage it. We always recommend using pedal assist on hill climbs.