Need help..... rear end noise

First off I apoligize for my stupidity when it comes to axle's/differentials, I can rebuild a motor with my eyes closed but never messed with rear ends or gears. Well I bought a 1996 2door 4x4 tahoe(7"lift on 35's) about 6 months ago and now the rear end is making some crazy howling/grinding noises. It has a slow leak on the right axle seal(i think that's what it's called, its leaking from the back side of the drum brake) but I checked the level and filled it up with oil. It makes the noise whenever I let off of the gas while driving or just barely push the gas(not under accel or stopped). Any help would be greatly apprecaited... I know I'm going to have to replace the axle seals, but just wanna know what else is bad in there.

Welcome to AF, this is typical of bad pinion bearings or an excessively worn ring and pinion. It more than likely have to come apart.( do the axle seal also )

Here is a link with some repair info on rear ends.
Not plugging there parts one way or the other.
But the info is good. MT
http://www.differentials.com/install.html

Thanks for the help guys, I'm gonna take the cover off and take a look tomorrow.

I had the same issue for over a year -- after coming to a stop, once I accelerate again a funny sound from the rear axle. At first I thought it was the rear drums sticking -- then the axle pinion -- then the driveshaft yoke -- everything checked out. Today I FINALLY found out what was making the noise!!!

http://www.granitecityperformance.com/media/TahoeAxle.png (http://www.granitecityperformance.com/media/TahoeAxle.jpg)

The front half of the 2-inch aluminum riser blocks on the axle gave way, the rear axle pitched up, trashed the driveshaft u-joint and clamps and as the axle twisted, sheared both brake lines.

All this time, the sound I was hearing was the springs shifting on top of the spacer blocks. I don't know if they are factory spacers or aftermarket but if you have aluminum spacers I would recommend checking them for cracks and make sure the U-bolts are secure. Luckily I wasn't moving very fast when it let go and I was able to "limp" home on the front drive...

I had the same issue for over a year -- after coming to a stop, once I accelerate again a funny sound from the rear axle. At first I thought it was the rear drums sticking -- then the axle pinion -- then the driveshaft yoke -- everything checked out. Today I FINALLY found out what was making the noise!!!

http://www.granitecityperformance.com/media/TahoeAxle.png (http://www.granitecityperformance.com/media/TahoeAxle.jpg)

The front half of the 2-inch aluminum riser blocks on the axle gave way, the rear axle pitched up, trashed the driveshaft u-joint and clamps and as the axle twisted, sheared both brake lines.

All this time, the sound I was hearing was the springs shifting on top of the spacer blocks. I don't know if they are factory spacers or aftermarket but if you have aluminum spacers I would recommend checking them for cracks and make sure the U-bolts are secure. Luckily I wasn't moving very fast when it let go and I was able to "limp" home on the front drive...

never use aluminum when in contact with steel this is very dangerous. as the two metals will cause an electric current to flow in the metal with salty water and then the al. will crumble completely.....if there was an insulating spacer "non conductive" this would not occur.......

The mode of failure was not from galvanic corrosion but from improper installation.

If you look closely at the photo, the previous owner used U-bolts with a rounded end instead of the correct square end. The U-bolts flexed, deformed and allowed the axle and blocks to shift, overloading the blocks causing a fracture. It was only a matter of time before they wiggled themselves out.

The mode of failure was not from galvanic corrosion but from improper installation.

If you look closely at the photo, the previous owner used U-bolts with a rounded end instead of the correct square end. The U-bolts flexed, deformed and allowed the axle and blocks to shift, overloading the blocks causing a fracture. It was only a matter of time before they wiggled themselves out.
I may be wrong but to me it looks like half the spacer is missing...I see the tab on the lower part of block and the rest of block is gone...also that al. looks very ruff not smooth and square cut as it should.

i can remember on an 1980's GM sedan al. spacers where used on the steel bumpers and this caused failures with the fasteners

Yes! The front half of both spacers are missing. At some point they cracked in half and the front pieces wiggled out and the whole axle spun upwards. The back half of the blocks are very solid and very dirty - coated with road salt. One swipe with my glove and they look good as new, what's left of them that is.

I have replacement blocks made of cast iron and the correct square-end U-bolts that I will be installing tomorrow. The new blocks are even tapered to correct the pinion angle!