Its hard to explain what it is. Its sounds like a tire thats a bit deflated and you get that wooing noise as you accumulate speed. But the air is fine on my tire, i also checked axle and thats fine, my next guess is ..Hub bearing and if thats not the case defected tire. But thats the weird thing i replace that hub bearing about two years ago and i also had a defected tire. the tire was a copper cobra and the nylon thread inside came apart and bubbled on the threaded area making my car hop. Wooing noise has been a few days now.