94 4x4 problems

when i have the 4x4 turned on i get what sounds like a thumping noise ,it comes either from the hubs or under the vehicle its hard to tell. it almost sounds like maybe one of the hubs are slipping or not engaging properly??? also when i turn the 4x4 off i get a whinning noise from the front end again it sounds like its in one of the front hubs . the only way to get rid of the whine is to pull it over andput it in reverse then back up a few feet. had no problems with any noise before this.

so you have automatic hubs?? I had the same problem with my 94 Ranger so i just got pissed and replaced the automatics with manual hubs..