Rear Differential or Wheel Bearing?

My Toyota Matrix (AWD/automatic) makes a “whirring” noise that comes from the rear of the car. It gets more high pitched at increased speeds. I’ve received 2 mechanic’s opinions: 1) It’s the rear differential 2) It’s a wheel bearing. Is there a way for me to tell who’s right or should I go for a third opinion?

Is this a 4 wheel drive Matrix? If so, it could be either a wheel bearing, differential or somthing dragging on the rear brakes.

Since neither mechanic knows enough to diagnose the problem, I would seek a knowlegeable third opinion, and have that mechanice drive the car first.

I had what I thought was a rear wheel bearing problem on a rear drive vehicle and it turned out to be the Positraction differential bearings. A $450 problem.

That there problem could also be a u-joint but usually a driveshaft is much older when it starts to do that.