Justin,

That sounds like ring and pinion lash is off, that is how you are going to get that howl, I just had this issue with mine...

Typically it is due to wear and possible bearing fatigue.

~Brian

So what does it mean if the diff howls??? Thans what mine does.... and it clunks really bad. For instance when I am driving normal, than I let off the gas, then tap it repeatedly.... it clunks with each tap of the gas. The bushings are nice and tight. Any solution??? The clunk is really bothering me, and my radio isnt loud enough to cover this noise up.

That is exactly what mine did. Finally it gave out and I got a new one and replaced my diff entirely. I opened up the old one and if you look in my gallery, you can see the damage that was done. I drove mine in the same condition you describe from February to August, then one day it just blew. It stopped howling and just sounded like someone was beating the bottom of my car with a baseball bat.

So, just replace the entire unit with a new one? I forgot to mention that whenever I hit a bump just right, it clunks too, but that could just be bad bushings.

I know I'm resurrecting this thread, but I have a question about my differential. My original 3.36 r180 differential was howling and making a horrific clunking noise (like someone was hitting the bottom of the car with a bat), so I replaced it with a 3.54 r180 out of a 280zx. I used the halfshafts from the r180, and bought a new differential mount while I was at it. The new differential doesn't whine, but a week after I installed it, I noticed a clicking noise coming from the passenger side rear upon acceleration from a dead stop. I thought it might be a bad u joint, so I pulled the right side halfshaft and replaced both u joints. The problem still exists, and I have no idea what it could be. I see on here that someone said that it could be suspension bushings that need to be replaced, and I was thinking the same thing. The clicking noise was accompanied by what sounded like a stress click, like the suspension was flexing.

This is fine and all, but the thing that concerned me was that when I had the differential out and the Z on jackstands, I was playing around and spinning the rear wheels. They were not connected to the halfshafts, so I assume they had no resistance on them. The left side wheel spun freely, and would spin somewhere around 20 revolutions, but the right wheel under the same force would spin maybe 5 or so.

I'm assuming this could be either a dragging rear brake shoe, or bad wheel bearings. I don't think it's a dragging brake shoe, because my rear brakes were improperly adjusted and wouldn't engage when pressing the brakes. Would bad wheel bearings cause a clicking noise upon acceleration from a stop?

Last question: I replaced the differential mount, and clunking was gone for a while. Now when I shift fast or when I let off and stab the gas, I hear clunking from the rear end. This sounds exactly like what the old differential would do, and the noise was gone when the differential mount was replaced. All bolts seem to be tight, and the mustache bar bushings are old, but seem to have some meat left on them. I did notice that the differential strap was a little loose, and had a slight tear in it. Is there any way to tighten up the differential strap?

I'm at a loss for ideas right now, and I don't want to start tearing pieces off of my Z and replace them for no reason.