I'm currently sitting in my MX, fully charged, ready to go on a mini-road trip and I noticed that my car is humming. Is this normal? It is silent outside - it's 215am, no one is awake. I noticed it earlier tonight too on my drive home to charge before I leave... Should I be worrying? It's louder than silent. Wow! I just jumped! My auto sensing wipers just wiped my windshield.. Totally just spooked Me! That's how silent it is... Except for this odd hum.... Any tips? Is this "normal" ?