2000 Buick Regal Humming/Roaring Noise at speed

Just started hearing noise (not grinding, but a humming or low roaring from the front that gets loader with speed, esp. 30mph and above. Continues when shifting into neutral, as long as we're rolling. Had tires checked - OK, rotated - no change, mechanic put it up on rack and did a number of checks, says it's not CV's, not wheel bearings, not engine, not tranny. Although mechanic said not classic wheel bearing noise, that what I'm thinking. Any ideas or same problem?