I have a very long write up that I am finishing up and I will post it very soon. Long story short this happened to me and I replaced the three bolt with a four bolt. I did a lot of test (millions of pictures) and both of mine checked out before installation. I have concluded at this point that it is the sound of the gearsets resonating through the rear subframe. I had upgraded to some adjustable uppers, a toe eliminator kit, and poly lower bushings.

I replaced the adjustable uppers with the stock uppers and it quitted down the noise a lot. This is what made me believe that it is noise that the old bushings absorbed but the new bushing just transfer. I hope to have the article up soon, but it is on my PC and I had to order another power adapter since my old one failed. Let me know if you have any questions and I will try to help.

Here is a link to My Build Thread.

Hope this helps and I will try to get the article up.

Robert

I'm having the same problem on my 1g as well, I noticed that the rear subframe bushings are pretty worn out so I ordered some new ones and I will be replacing them soon, I'll let you know if that fixes the problem.

Thank god it's not only on mine! I also swapped to Ingalls adjutable upper control arms so your explanation seems appropriate. I will read your link and try to figure it out. Thanks a lot, really appreciated

The differential article is not yet posted. I have to catch the build thread up by editing a few more videos before I can post the Diff article. It should be up within a week or so.

Robert

Awesome!! Thanks a lot!

To add: I installed the poly rear bushings from tuners nation on my 1g a year or so back and there was incredible noise on decel from the rear diff. I actually hunted 2 others diffs down to compare with and had the same results, so dont be surprised if its still bangin' on decel with new bushings. I do have a twin clutch (unsprung), Id be curious if people with sprung disks do or dont have this issue.

I run a Southbend TZ/FE sprung disk from TMZperformance and I had the noise in two rears that checked out to the specs in the book so I do not think the clutch disk is the cause.

Robert

Solves that I guess - did you fill your carrier bearings?

I did not fill the carrier bearings, but I did fully rebuild the driveshaft. The video below is part 3 of a 5 part series. Even after this and a few other fixes the noise persisted never changing a note.

Driveshaft 103 - Replacing carrier bearings - YouTube

Robert

I run an Exedy OEM Spec Clutch and pressure plate and still have the sound coming from the rear diff. I also have brand new carrier bearings. Maybe I should replace all 3 U-joints and see if it does a difference... Oh, I also have stock rear bushings with Ingalls Adjustable upper control arms.

I just finished installing the new subframe bushings but the noise is still there.

hey guys! i know this is an old thread, but i just put in the aluminum/poly diff mounts in last weekend and my car is howling on deceleration as well, although when i put the clutch in all the noise stops. this the same for you guys?

Yes, this is an old thread but I'll jump in on it with you, as I'm also trying to diagnose a rear end whine in my 93 tsi with lsd, adjustable uca's, poly bushings all around, toe eliminator, rebuilt driveshaft, and new wheel bearings.
The sound I'm hearing appears to be coming from the rear diff, only while coasting, and in gear. Not during acceleration, or deceleration.
After reading a bunch of threads;
including these:
http://www.dsmtuners.com/threads/rear-diff-howling-noise.190588/
http://www.dsmtuners.com/threads/whining-from-rear-of-car.450393/
http://www.dsmtuners.com/threads/rear-diff-wineing.35935/

There's a few diagnoses that might possibly explain what we're hearing.
1. Acceleration only- gear issue
2. Coasting- bearing issue
3. Could just be "a DSM thing"... Numerous people claim to hear this noise on perfectly fine, functioning diffs

Once I figure mine out, I'll post back. Anyone else please do the same

okay yea that makes sense. Before i swapped out my horribly deteriorated rubber diff mounts I always thought i heard something on decel, but it was just soooooo quiet. Now that ive put in solid mounts i realize that its the exact same noise i was hearing just amplified like crazy. I want to find oem diff mounts and put those back in, but you cant find them anywhere.

It's a dsm thing. Lightweight clutches with inadequate damping in the hub. If everything was brand new/nice and tight it would likely make the same noise.

Definitely being caused by flywheel/clutch aftermarkets and poly/ solid bushings. Ive got the same decel noise at certain rpm and its likely caused by rear toe eliminator kit being solid metal and metal carrier bushings and poly rear subframe bushings.

It's not caused by solid bushings, it's just transmitted to the car better with them

It still could be an excessive backlash issue at the transfer case or rear differential ring and pinion, but solid bushings amplify the harmonics quite a bit.