Mechanical whirl in back right tire of my 2001 ford escape

I've taken my vehicle to two different mechanics, and I keep getting the same answer, they dont know whats wrong with it. Two nights ago I was at a stop light, when I began to accelerate, I heard a pop under my vehicle. I honestly thought I ran over something and possibly popped my tire. I arrived at where I was going, checked the tires, and noticed nothing out of the ordinary. When I got back into my escape, and started driving, I noticed resistence in my steering, almost like my vehicle was stuck in four wheel drive. The next morning on the way to work I was on the interstate and reached around 70 mph, I could hear a loud mechanical whirl coming from my back right tire. The loud mechanical whirl became louder so I pulled off on the side of the road. As I was applying my brakes, there was a very loud almost screeching coming from the right side of my vehicle. Im really not sure whats going on, but it almost feels as if my vehicle is stuck in 4 wheel drive,  yet everytime I've had 4 wheel drive engaged, I've never heard the mechanical whirling that I'm hearing now. My mechanic replaced my brake shoes in the back earlier today, but I'm still hearing the sound. Can someone please help?