Ooms

As the title states, I have a rattle, not fast, like dropping only a handful of marbles on metal. This only happens off power, dropping from 4k-2k rpm with the clutch engaged, any gear except neutral. (ok ok, I know its not a gear, but that still allows me to check the clutch engaged part) There are no codes and CEL is not on. The sound goes away if I gingerly touch the accelerator, I think. Wind noise is making it hard to hear.

This is a 96 A4 Quattro 2.8L V6 12valve, 118000 miles. I lowered the exhaust to remove the heat shields, as well as the front belly pan to bang around, and the only thing that I currently find that rattles is one of the cats (I think.) Its very hard to tell which one, but its not a typical bad cat rattle (which would be more like a maraca I guess). The heat shields and exhaust were not loose, nor does it seem like they are hitting anything.

Its near impossible to tell where a sound is coming from while in car, but if I had to guess, it's in the middle; driving with my head out of the window like a dog ;-)

Typically a bad cat will rattle regardless of clutch engaged, as well as making noise almost constantly, so that leads me to believe it is not related. I will try to get a sound clip, but I have to be moving, so wind noise will be a problem.


Shortly, in a month I will be replacing the timing belt and associated parts, and this week the front outer CV boots, which will allow me to dig deeper. There is no loss of power, nor vibration felt in car.

Any ideas?

Ooms

Bump. Still looking for ideas.

Ooms

Forgot to mention, the driveshaft center bearing support feels fine as well, the rubber is still good.

AMJ

Pretty sure that's indicative of a bad front prop shaft cv joint. I have the same issue on my 96 A4, it's been there since last fall, getting worse. I have the new cv, it's on the schedule to be changed in about 2 weeks.

Apparently, the heat from the exhaust cooks the grease in teh front cv making it toast.

Ooms

That's not it on mine. Replaced boots all around recently as well as the left front CV shaft due to me breaking it. Don't ask how, I am embarrassed to say LOL.

It's definitely small backfires. I searched the forums and found posts about many Audis having this problem. No solution to be found.

AMJ

Never heard of the backfiring issue - but I haven't been on the boards much.

Just to clarify, I was referring to the cv joint on the forward half of the front-to-rear driveshaft (transmission to differential), not the cv's on the axle shafts. Just something to keep in mind.

Ooms

Oh yes, I checked those as well. I just did a search for backfire and came up with quite a lot of threads about it. One user, VAP I believe, claimed he would figure it out for everyone...then up and disappeared.

Ooms

So, yesterday my drivers side cat went. Rattled like a tin can filled with marbles. Replaced it and no more rattle as bad as the orig post. So I was wrong, the cat was breaking inside, but ever so slightly in the beginning. I still have a slight, and I mean VERY slight backfire noise, or possibly the passenger cat doing the same, but you have to know it's there beforehand to even hear it really. I know it's rare for a cat to break inside. Just thought I'd finish up the thread.

AMJ

After you mentioned that it might be backfiring, I actually had the misfortune of my driver's side exhaust breaking just after the cat. The rattling noise (backfiring) got noticably louder. Rewelded the pipe, and the noise is significantly quieter again.

Thanks for the update - I guess my cats are likely cooked as well. Did you replace with aftermarket?

GTHMH

I had the same problem at around 140,000 miles.
Replace both cat with aftermarket stuff.
No more rattle, but I still have pretty big backfire on decceleration.
I read from either bentley of chilton manual that small backfire on this car with engine break is natural... Still annoying tho.