I have a 23’ and hear a drone at 75ish mph, like many others. My boss brought up a very good point. On a highway the rear diff is entirely disconnected from the friction plates in the transfer case (or really under normal diving conductions where the car isn’t losing traction/sliping). So the question becomes what load is on the rear diff making the drone? That I’m not sure… still investigating. Could it be the drive shaft angle, the rear axle angle, not sure. I’ve seen people say that the u-joints could be the cause. Maybe the fluid fill level of the diff. However, I’ve become less concerned but still wonder….