It's been howling for ten years. Constant. It's been inspected twice in that time and no damage is seen.
It's getting worse. Should I bring it to a specialty shop and have them rebuild it?
TIA,
Vince

 

Have you checked the fluid level? If it's OK, you might want to change it.

 

Bad bearings won't howl for 10 years unless you only drive 500 miles per year.

More likely it is the ring and pinion. It is unusual for a factory diff to howl due to poor ring and pinion set up. Not impossible, but search the threads, it just does not come up. Bearings yes, as there were lots of those issues in rigid axles and IRS.

If it is getting worse, you can get it redone. R&P, bearings, labor, expect north of $1000.

Beware cheap or inexperienced jobs, as you'll have a howler again in short order.

 

The 2002 with 4 x 4 has an independant rear axle. The pumpkin is mounted to the truck body under the rear seat. Mine had the small howl for 10 years also. I think its the gear set mesh and the resonant frequency with the body mount. REcently it has started to get louder and i checked to see that the pinion bearing is starting to get excess clearance. I also think a good rebuild and proper gear setup would help a bunch.

 

Yep. It lasted this long. About time for a fix.

 

It was the rear wheel bearings! Damn.

 

I have been looking for a solution for this problem beginning in 2002 I found it on 3/10/2014. Ford makes a kit to correct this problem amazing consisting of Pinion bearings front and rear, seals, large and small pinion gears and a shim set for the pinion gears there is several other smaller items also. There is a TSB covering this it is TSB 05-23-3. I have replaced the axle bearings on several trucks with little results in noise reduction.

 

Mine was caused by the wheel bearing. After I had it changed, no more noise....so far.