I hear 2 distinct sounds, one sounds like an RC car,
the other like ripping cloth.
The first would be the motor, the latter the tire. And it is an interesting sound at that.
BTW, slightly off-topic, but is anyone else tired of hearing about "silent" electric cars? All the ones I've seen make as much or more noise than some quiet gas engines, and I rather like a car that lets people know when I'm moving. As in a warning to other drivers and pedestrians, yes, I really am accelerating at a rate of 32fps^2