The vibration noise you hear is usually caused by bolts coming loose over time. I would go through and tighten all of the bolts inside and out. The magnetic coil ballasts vibrate during normal operation. You could have loose bolts inside the ballast compartment (holding the capacitor, magnetic coil) or it could just be the hood cover. Magnetic coil ballasts might not be as efficient as the digital lights, but they do last a lot longer.