Diagnosing differential Problems? (or transmission)

[Bobble]

I have a 2g gsx and my transmission or differential has been making a howling noise during all acceleration or deceleration. It finally failed the other day and it made the car immobile because it would cause a jumping in the drivetrain. Because it was making a noise constantly it leads me to think it was the differential. However how can you tell if it was the front diff or the rear? Any help is appreciated.

I have already taken out the front axles and the driver's side axles is worn on the transmission end.

 

[thirsty]

You need a jack, and 2 jack stands. Jack the car up at the rear by lifting the diff. Put the jack stands under on the jack points under the car. Get a mate to turn one rear wheel, with the car out of gear, as you either turn the other wheel in the opposite direction. Watch to see if the tailshaft rotates. Listen for noise.
Cheers
Ross

 

[Bobble]

It doesnt make any noise in the front or the rear wheels when you jack it up and spin the tires. The tailshaft is rotating. Also, the noise would only occur when it was over about 15 mph.

Should I got ahead and remove the t case and look at it? What do should I look for? Same thing with the rear diff, should I remove the cover and what should I look for?