I have a humming that starts around 40 mph and gets louder with speed. Not engine related as the sound remains when I take my foot off of the accelerator. Noise temporarily goes away in a right turn but returns when I straighten the wheel. Dealer suspects Wheel bearings and they aren't under warranty at 50k miles. Does this sound like the right problem and is it true tat Wheel bearings wouldn't be covered under 3 years old?