I have removed the flaps from the damper and I still hear the vibration. What can I do to fix the issue?
If you still hear vibration, please make sure that the unit is installed using a rigid/metal tube for the range hood to have a better efficiency as well as to preserve the life of the motor. Also, by using a rigid duct tube, you will save energy.  If a rigid duct tube was used and you are still having issues, it can be that the motor is unbalanced and would need to be replaced.