As the car speed increases, at about 50 miles per hour, a loud hum comes from the rear wheel area. When the speed get to about 60 the sound goes away. Outside of the 50 mph speed, the car is very quiet. The card does not shake at any speed. Tires have not been rotated for aprox 11,000 miles. I do not see out of the ordinary tire wear on any tires.
My car has 80000 miles.
My car has an automatic transmission.
This kind of hum sound generally comes from tires that may be out of balance or which need to be rotated; however, if you have just rotated them recently, this should not be an issue unless you have an odd tread wear pattern developing.
This may also be a bad or failing wheel bearing which can also cause this type of hum sound from metal on metal grinding of roller bearings. These bearings are machined and designed with very tight tolerances and, when they are not properly lubricated, they can generate an enormous amount of heat which is what ultimately causes them to fail.
I would recommend having an expert, such as one from YourMechanic, come to your home to help diagnose the sound that your car is making.