At 213K miles my LX has developed an audible rumble at specific speeds. As I approach 70 mph the rumble begins. As speed increases the rumble fades away until something like 78 mph where it returns somewhat, and then fades away if I travel faster. It's 98% audible as I don't feel it in the steering wheel nor in my butt. Swaying gently doesn't influence the rumble so I've generally discounted wheel bearings and somewhat the tires. I recently replaced my rear driveshaft with OEM and inspected and lubricated the front shaft, but that didn't change anything. Everything is right-and-tight with the steering components and rear end control arm bushings. Tires are Michelin all season, are a couple of years old, and tread wear is normal. The front wheel bearings were replaced at the last brake service about 10K miles ago. I've begun to think it may be the rear differential but I'm just guessing and I don't like to do that. Thoughts? Experiences?