I just bought a 2015 Smart Fortwo that had come in after a lease and had only 16,000 miles on it. The busy area where I did my test drive was quite noisy so I did not notice this faint noise until I drove it home on Tuesday. It is a faint high pitched whine that happens when I accelerate. I am trying to tell if it has anything to do with the AC being on, the fan, etc. Is this normal? What steps would you take to diagnose? Carmax will take care of it within the first thirty days and I still have until November of this year on the manufacturer's warranty. I am happy with the car in other respects but would like to get this resolved so I start with a clean slate. Thanks in advance for any ideas.