Driving around today, I couldn't help but noticed a rubbing swishing noise coming from the rear of the car. I am driving a 2012 MR with stock wheels and tires. Seems to be tied to the speed of the wheels and tires. Looked under the car for any leaks and couldn't see anything. None of the tires have any air coming from them. None of the calipers look like they have any clearance issues. Tried pressing the brakes while moving to see if the pads might be dragging and that didn't alleviate the sound. Nothing was obstructing drive shaft or prop shafts. Any help would be greatly appreciated...

 

Could it be the rear diff making that noise?

 

Probably something nasty stuck to the tire tread. Asphalt maybe.