I just had new tires put on so I know it isn't my tires or sounds from my tires. I think it is a wheel bearing but noboday can seem to "hear" the sound. The stearing wheel doesn't feel tight and sometimes randomly swurves. I don't know if it is a bad wheel bearing or the rack installation I had done 6 months ago. Everyone that has been under it says the rack is fine. Something is wrong though.