Q: The rear end roars the faster i go in my 1996 Jeep Cherokee.

It isnt too bad when driving around 20-30 mph. But when increasing speed it gets very noticeable. It's really loud on I-75 when getting up to 75 miles per hour. And it sorta has a shake to it that will die out once around 70-80. But the noise stays. I was thinking the u-joint my be why it's shaking so I'll be having that replaced any way because I all ready baught it and the shaft did have some play too it. But i was thinking just to change the rear wheel bearings my self and have a mechanic change my pinion Bearing for me. My tires dont have much play to them. When i jack the back of the car and spun the wheels the did spin for a little freely, but did sound ah little gritty, Not alot. when i disconnected the rear shaft from the rear end and turned the yoke it had a slide grinned to it. Anyway when speeding it like ruuuuuuuuuuuuuuummmm until I slow down to like 20mph. Could it possibly even be rotors ?? Its not crazy noticeable at low speeds. Sorry for confusion. Really want to fix it

My car has 220000 miles.
My car has an automatic transmission.