OK, this one has me stumped so far. My 2007 Escape Hybrid, 59,000 miles, makes a whirring or whine sound at highway speeds when going straight. (it sounds similar to axle gear noise - about 300 to 400 HZ) If I turn the steering wheel to the left, it gets much louder. If I turn to the right, it nearly stops. I jacked up all 4 corners and grabbed the tires and did a wheel rocking test. The right front wheel had play so I had the wheel bearing and outer tie rod replaced. To my shock, the noise is totally unchanged! Now it is getting louder on a coast as well as turning left.
Tires have about 5000 miles - Conti CrossContacts.