If there is a vibration or noise at highway speed, it could be from the front driveshaft and may require replacement of the double cardan joint. A double cardan joint is a type of driveshaft joint that uses two universal joints.
Car Problem Reports
Ford Bronco Problem With Double Cardan Joint May Cause Virbation/Noise at High Speeds
Ford Bronco Problem
Drive Train Affected: Automatic Transmission
Average Mileage: 142,500 mi (35,000 mi - 250,000 mi)
Visitor, 1995 Ford Bronco, Automatic Transmission, 250,000 mi
front double cardan u joints loose and front drive line loose
vibrates and rumbles at around 45mph when front drive shaft is engaged in 4x4 and in drive until truck is backed up to disengage front drive shaft.