a strange noise similar to a beaing going out

I accelerate up to 20 or greater and the houling sound begins. I let off the gas and it does not change, I apply the brakes and it does not change, I also steer back and forth and no change in the sound. The trans shifts fine. I mainly travel highway 65-75 mph every day. When I get below 20 the sound seems to go away. I also do not feel any vibrations. If you can help I would like to donate then. Oh, I have had no problems with this car since I bought it new.

thanks