The truck is a 4x4 with 210000 miles on it. I crawled under the truck and checked that front drive shaft is not engaged. Any help would be greatly appreciated.
1999 for ranger has a whining noise driving down the road. on 1999 Ford Ranger
If it sounds like a single prop plane flying outside your vehicle that gets louder as you go faster, probably a bad wheel bearing or more than 1 wheel bearing. Common issue for the ranger with age and mileage.