I just purchased my Nissan Sentra 2011 about two weeks ago. I started noticing some strange grinding noise when I first start driving the car. It happens as soon as I leave the parking space. At first it sounded like my front bumper was grinding on the sidewalk but clearly I was in the center of the road. So then I decided to check the engine and underneath to see if there was any loose parts that might be hitting each other, nothing everything was clear. The car only does it when I start driving it after it has been shutdown for more than a few hours. Also the car only does it once for a few seconds, it seems like such minor problem but the car is brand new it should not be making any strange sounds. Also I check the road that I usually drive on for any holes or debris and it is all clear.