Noisy Rear Gears, or What

[Frozen_Bohemian]

Just swapped out the 7 1/4" rear end in my 65 Barracuda last week because it was making noise. Found a used rearend that had been sitting a long time and swapped it in to have the same noise. I cleaned out the new(old) rearend (had some rust on the ring gear but mostly it was just cruddy inside) and used new gear lube. I used the axles that come with the rear too.
The noise is not as bad as before but still there. I know this was a low mileage rearend and except for have been stored outside for a long time I assumed it was good.
I cannot believe I have 2 bad rear ends, so now I need to figure out what else the noise can be coming from. Not the transmission the sound is from the back of the car, what about the driveshaft? If the u joints are crapped out would they be noisy or just start to clunk and shake?
Any other ideas?
Will it quiet down after being run awhile if it there was rust on the gear set or bearings?

 

[cudamark]

If it's a constant rumble sound, it's probably an axle bearing. If it has a whine and/or changes pitch when you accelerate/decelereate, it probably ring and pinion. If it's pinion bearings, you can usually feel them bind as you rotate the pinion flange by hand. Pull the driveshaft loose and rear drum off first so nothing else can be binding. You can usually narrrow down the location by getting the car up in the air and checking different locations with a stethescope or wooden dowel up to your ear while the car is running in high gear. Just make sure the car is securely on stands with front wheels chocked and nothing/nobody in front of the car that you don't want to run over! Oh, bad gears and/or bearings don't repair themselves....if they're bad, they won't get better, only worse.