Brozee

Hey all,
A co-worker of mine pointed out that the sound he heard when I started my car was irregular. He said it sounds like an exhaust leak. When I start the car from a cold start, or after the car has been sitting for a few hours, it sounds like a low humming motorcyle'ish noise coming from beneath the middle of the car. As soon as the car is warmed up, or about 15 seconds after starting the car, the noise and everything to do with it is gone. Is it even worth looking into? I have no issues whatsoever with the car running, it idles perfect; actually a very smooth idle unlike a lot of members on here. The car is also quiet when at stops and etc, it's only when the car is started first.

MP4.2+6.0

I had that kind of issue--back to my 5000 in the mid 80's--but if you hear it cold and but not when warmed up, I would look at the joints on the exhaust system around the area you think you are hearing it. Hearing it all the time would be a yet bigger leak, or perhaps a crack or blown part. Good news is that the "only when cold" diagnosis is more optimistic for just a loose part.

Either get under there for a cold start and check it out, or have a shop look at it. You are searching for the leak either by sound and/or the feel of some air coming out of a joint somewhere. Often you can just tighten one of the connection point clamps where you find an issue and fix it, after spraying on some penetrant and letting it soak in a while that is. Back on the 5000 it used some finicky sealing rings and sometimes you would have to take apart the joint and use some high temp sealant on it. When I pulled the downpipe on my A6 4.2 for some cylinder head work, it just seemed to bolt back together cleanly.

Brozee

Thanks for the reply. After taking this video I noticed I can smell it if I rev the engine, as well as it gets pretty loud. Again, only on initial start-up though, I don't notice it one bit at red lights, stop signs, or general driving. Here's a video with the noise. (Don't mind me and my roomate discussing it lol)

http://youtu.be/m0LUYFs90AI

mishar

Go to the first muffler shop and they will tell and show you what's wrong.

MP4.2+6.0

Sounds like it is pretty far forward just from the apparent volume, and what may be one cylinder sound. I would be looking at before the converters, and maybe as early as the exhaust manifold. Could be a cracked part too. where the crack pretty much closes up when the part warms up a bit. The converters light off in the first minute or two, so the temps go up rapidly in the front sections.

Mister Bally

Can also be one of the flex pipes as they are a known weak link. There is a $10 wrap-around fix that works well available at most auto parts stores.

Brozee

Took it to a local muffler shop and they said it is a leak due to the flex pipe. They are removing it and replacing it with a new one tomorrow morning. We will see what happens.

FlyTyinFool

Geez... And I thought the automatic parking brake adjustment cacophony every 800 (or so) miles was annoying.

Sounds like it should be an affordable fix though. I'll keep my fingers crossed for you.


Carry on...

Brozee

Turns out it was the driver's side flex pipe. Took it to a local muffler shop, they removed the old one, fitted a new one and welded it together, passenger side was fine. Total was $150 + tax.

NotoriousGLU

Seems I have same problem with my 2007 S8. We went to KY last weekend and on the way back I noticed that my car sounds like there is a hole in the exhaust lol. Similar sound to your problem.

I am taking it to local muffler shop to get it fixed tomorrow

I think I will record how it sounds to let rest of S8 owners how it sounds. I could not find any extra info except your post.