I experienced a first the other day, a Gatorskin tire with 5,000 miles on it. The wear indicators were gone, but it still had rubber on it. I had a replacement handy for the next time I had to fix a flat or work on the wheel at home. But it started making a whining noise at high speed, more noticeable at lower pressure. I replaced it and the whining went away. It must have been some kind of tread separation. Anyone else ever experience this?