One of our cars has developed a roar coming from the back passenger side. This occurs only at speeds above 55 MPH. There is no play in the bearing and the wheel rotates without any detectable roughness when spun by hand. The roar comes and goes with a period of about 1 minute. The roar is only slightly modified by turning the car a bit to the right or left. I've never had a bad wheel bearing present in quite this way, so I appeal to those with much greater experience: Can this roar be caused by a bad wheel bearing? The problem is not the tire as I have rotated the tires without any effect on the roar. The bearing in question is a National bearing replaced by me about six years ago. I used a torque wrench to install it. Were the National bearings of about six years ago of poor quality.? The bearing has about 30,000 miles on it. Thanks for any help with this question.