right rear metal to metal rattle sound
 

I have a rattle in the the right rear of my 2002 A8L everything passes visual inspection. I literally removed everything from trunk including spare tire, removed the rear bumper. I have changed out rear brakes and have eliminated loose brakes because I still have a metal to metal rattle sound with the parking brake dragging while I drive car over bumps. I removed the shock absorber and the noise was almost gone so I replaced with a known good one, same metal to metal rattle. Now the crazy thing is that I just bought a 2003 A8L with same noise! So I will tell you that I Have owned 2 97 A8s, a 98 A8, 2 2000 A8s, 2000 A8L, 2001 S8 and my current 2002 and 2003 A8Ls. Yes that is 8 D2s in the last 7 years. My best friend loves my A8L so much he bought a 2002 and his nephew bought a 2001 S8. So I have been wrenching on 10 D2s. I have never had this noise except these two cars. I need to solve this problem so I can sell my 2002 and put the smile back into driving my A8L. I don't have the special spring compressor or I would have removed the spring for a better inspection.
Any Ideas?

It could be the exhaust perhaps? Or more likely a splash guard (if that's the right name) on the brakes. They can easily be bent when fitting new brakes and will touch something.

Or it could be stone stuck somewhere above or inside subframe

Sounds exactly like a rattle I had a few years ago.

Took ages to find what it was. Sounded like the exhaust or a loose heat deflector underneath the car.

Mine turned out to be incorrectly fitted rear pads. I believe the clip that holds them in place was in the wrong position. At first inspection they seemed to be tight and correctly fitted and the noise seemed to be unaffected by braking, yet the noise completely disappeared once they were refitted correctly.

I've had similar noises when the dust/heat guard catches on the disc, but that's usually quite a speed-dependant noise. When the brake pads rattle it's more road surface dependant.

My bet is on the heat deflectors.

Broken spring. Sounds like the bottom coil has snapped off and the broken ends are touching and making a noise. I had the same thing on my D2 and our TT :)

I was thinking dust shield around the disc like others until I read this^.

I had the very same maddening noise on my old e46 3 series, and it was the rear coil that had snapped at the bottom. I'd forgotten all about that until I read MikkiJayne's comment. Simple enough fix. I bought some spring compressors from eBay cheaply enough. Fine for occasional use.

I had that too on my first '8. The side in question was a little lower, which is what gave it away.

Yeh, the spring is a good call. My sons 17yr old Honda CR-V had both springs go within a few months of each other and as as they broke in the cup at the lower end it was hard to see until it was totally jacked up with weight off the wheels.

Thanks for the quick responses. Positive it is not the springs confirmed that has all coils. Had three sets of 269 mm rotors two drilled & slotted and one smooth. and two different oem type semi metallic pads and one set ceramic with tapered edges. Didn't notice a lose dust sheild when I changed the rotors.

The sound is very much like a sloppy set of brakes but 99% sure not brakes.

The exhaust is properly supported via the rubber hangers.

Next least expensive step is to pull the exhaust and heat shields and inspect the driveshaft center carrier. I think I'll order the rear output seal for transmission because I will right there.

The street I live on is concrete that has cracked so the city of Toledo has patched with asphalt. So I have little bumps every 15' to rattle this issue and remind me...:Confused:

Any other thoughts or ideas is greatly appreciated Thanks

Pads rattling in the carriers? Ie worn carrier rather than anything peculiar to the pads themselves.

Had a similar noise on FL D2 S8 when the cats started breaking up internally.

Had that too. Open the door, stick your head out and rev the engine. Rattling cats should be obvious if that's the problem

Very obvious indeed. I bought my current S8 with a rattling cat. Though by the time I finally got round to replacing it the rattle actually stopped - nothing left inside!

Not rattling cats.

On brake carriers there was some indentations where the pads rest so I kissed them with grinder to smooth them out. the springs on top of the rear pads keep them pressed tight. This moves pad toward center a fraction. I also switches carriers left right because one of the guide pins are usually slightly sloppier than the other because of the direction of rotation.. I have done this same treatment to all my Audis and friends cars also. Great success with no down side on any other cars. Probably 20+ cars in 10 or 12 years. In fact more even pad wear. Had rattle before and after carrier swap/treatment

I When I stripped the entire trunk of everything and even removed rear bumper. I rode in the back seat leaning out the window. The sound appeared to come from the right rear wheel well (although I didn't actually lean out the drivers side...hmmm bet it sounds horrible on that side also).

I am down to the rubber surround on the center driveshaft. It is probably deteriorated to the point that it allows contact. Funny that I have some vibrations on highway but nothing major. I also live in area that I seldom drive faster than 50-55. Mostly country roads without long stretches of smooth pavement. I always blamed vibrations on low profile tires and road surfaces. I think the sound must echo down the tunnel created by heat shielding. My street is the acid test of vibrations. When I have the windows down and hit bumps people turn and look. Sounds like a garbage truck.

I'll be doing exploratory disassembly when I get the rear transmission output seals and get some picks when I find root cause.

thanks for all suggestions.

Something that might help locate/eliminate sources: Attach a cheap GoPro type camera underneath, pointing at anything you suspect might be the cause.

You need to get it on one of those 4 post road simulator shaking lifts, not sure if or where are they available in UK but some countries use them for MOT equivalent tests, I think one of them is Germany.