If someone (e.g.- previous owner, oil change shop) overfilled the diff, then it could be the oil leaking out onto the brake shoes, as Sheriff said. I have seen the seals on the axles not hold this, and it gets past those and into the rear brake drum.

It make have glazed the shoes such that the sound went away (or never really developed) when going forward, but "rubbing against the grain" may produce the squeak.

As others have pointed out, the u-joints typically clunk or click, not squeak.

If it was diff-related (gears, carrier bearings) it would likely make the noise when turning either left or right, but possibly not both. Also would probably not make a squeaking noise. Forward or reverse would not usually make a difference.

Could also be wheel bearings, but I would look at the brakes for the fluid leak, and check the bearings while you are in there.

 

Well after spraying the u-joint with some wd40 a few times the noise has gone away. I'm not sure what to do now, forget about it or replace it anyway. I plan on parking the truck this winter to do some maintenance anyway, I'll just wait until then to pull the driveshaft.

Its funny that you mention the rear brakes. A couple weeks ago my truck developed a severe vibration in the rear end while braking. It feels like warped rotors, except its coming from the rear. I don't feel it in the brake pedal, but it's impossible to make a smooth stop. You can actually see the rear of my truck bouncing up and down when braking hard. I don't think this is related the the squeaking, but it is an issue all the same.

 

Not to thread jack you, bit what about a clunk whwn I put my 98 4x4 in reverse?

 

That's normal for a dodge, don't worry about it.

 

squeaking u-joints is the first sound they make when going bad. its and indication that the grease has slung out and its DRY.
after it wears out, it will eventually click, then clack.

if you had greasable u-joints right now, you could grease them and they'd be fine.

 

Good info in this thread all around. There's a reason this is my 1 stop for my truck.

 

When I first got my truck, the brakes felt HORRIBLE. No matter how lightly you stepped on the pedal, the rear would generate a massive vibration. When I pulled the drums to inspect, the shoes were worn to the point that the rivets were digging into the drum, causing the vibration. Redid my rear brakes, problem is gone.