A whine has developed in my 95 4x4 Dakota. It doesn't happen when the power train is engaged. It happens when I push in the clutch, or coast in neutral. If I slowly decelerate by backing off the accelerator, it doesn't make the sound.
It the kind of sound you get when you downshift. But I'm not downshifting. It is coming from the back end.

Differential? Driveshaft?

Any suggestions?

 

If your positive it is coming from the rear, then start with the rear end. Opening it up and looking at the gears is best. Make sure it has the proper amount of oil.

 

Update: I checked the fluid level at lunch. It was a bit low. I added 1/2 quart. I noticed it looks like it's blowing out the front seal by the Ujoint.

According to what I found on this site:
BEARING NOISE
The axle shaft, differential and pinion gear bearings can all produce noise when worn or damaged. Bearing noise can be either a whining, or a growling sound. Pinion gear bearings have a constant-pitch noise. This noise changes only with vehicle speed. Pinion bearing noise will be higher because it rotates at a faster rate. Drive the vehicle and load the differential. If bearing noise occurs the pinion rear bearing is the source of the noise. If the bearing noise is heard during a coast, front bearing is the source. Worn, damaged differential bearings usually produce a low pitch noise. Differential bearing noise is similar to pinion bearing. The pitch of differential bearing noise is also constant and varies only with vehicle speed. Axle shaft bearings produce noise and vibration when worn or damaged. The noise generally changes when the bearings are loaded. Road test the vehicle. Turn the vehicle sharply to the left and to the right. This will load the bearings and change the noise level. Where axle bearing damage is slight, the noise is usually not noticeable at speeds above 30 mph.

How difficult is this fix? I do most of my own wrenching, but I've never dug into a rear diff.