Hi everyone! I'm posting this for my mum. She doesn't exactly notice odd sounds and behaviors in cars and I caught this as soon as she started it in the garage. After driving it a bit myself, I have noticed that basically whenever the RPMs are between 1000 and 1600, or anything above idle, there is a loud rattle and almost like an electric hiss coming from the engine area. It is most evident after the engine has been revved and the RPMs are falling to idle, but when it's in idle, nothing.

 

Did you ever find out the cause of this rattle? Just started happening on my 2012. Only happens when RPMs are falling off. Almost sounds like an exhaust heat shield is rattling.

 

No I did not. It never really bothered her enough to get it taken care of. I think it should be because it is probably a simple fix for something that sounds kind of bad, but I think when it is due for inspection I will remind her to mention it and it might just be a heat shield (hopefully haha).

 

I got this diagnosed by the dealer and seems to be coming from inside the center muffler. Right now, the problem is very limited, so it's not worth the money. If it ends up throwing an emissions code, it will be covered by warranty anyway. Playing the waiting game for now.

 

Thank you for letting me know about that. I thought I read somewhere that someone said it was coming from inside their catalytic converter but then again, any of those parts could make a noise like that if something is messed up inside. I will post back if we find out what our problem is.

 

Quick update. I ended up taking the car to a trusted exhaust shop and they were able to find a crack in the first joint for the exhaust pipes from the 2 banks. There is small 1.5 inch metal piece that kind of acts as a brace whose weld had broken and was rattling in its place. How it managed to stay there despite having broken off is utterly surprising to me.

We ended up welding that piece and another crack we found and also added a strip of steel to hold the two pipes under tension as if someone was holding them as close together as possible without trying to damage them. This took care of 75% of the rattle. I think there is still something in there that is broken and rattling when the resonance happens. My guess is that the vibration of the pipes itself might be a standard occurrence. Its the loose matter inside that managed to get in there that is causing the sound when the pipes vibrate so much.

 

Catalyst,

Our car was recalled for a leak in the fuel rail that allowed gas vapors to escape, so while we were dropping it off, we noted that there was a rattle under certain RPM. Surely enough, after replacing a muffler and some other pieces from a weld that had broke, the rattle was completely gone. After looking up the part numbers from the service receipt (which was all warranty work so no charge) from parts.audiusa.com, it would have been around $600 in parts alone!

Luke

 

Luke, thank you so much for your input. You have no idea what you just did. You are the first person to confirm online, at-least that I know of, that a replacement muffler section is the solution and NOT the CC.

Should things get worse, I have decide to have the local shop cut out the mufflers and check for loose pieces in there. That would still be a whole lot cheaper than the replacement section + labor.

 

Your best bet is to get under the car and hit the exhaust pipes with the side of your fist and listen closely for rattling. Depending on the engine in the car, there are numerous heat shields that can rattle because of their placement. They are easy to bend so if during the assembly process they were slightly off it might have gone unnoticed.

Personally, I would not be cutting apart an exhaust system that is only 3 years old. This is a red flag in my mind that either something is really wrong, or a misdiagnosis.

 

Thank you for your reply. We already tried that without luck. We used a rubber mallet. We put the car up on a lift with a person in the driver seat revving the car up to the exact RPM where the rattle happens. Nothing on the outside is doing this for sure. It is definitely something inside the exhaust section containing the mufflers in my case. However, we were unable to pinpoint left/right muffler because of their proximity.

Cutting exhaust pipes and welding them back up is nothing new, I have had it done in the past with another car. It is quite cheap too. While my vehicle might be only 3 yrs old, it already has 65K+ miles on it and out of warranty. Everything else is now mechanically sound from various visits to the dealer/performance shop/exhaust shop. While other people have had this issue, I don't know of anyone out of warranty trying to find cheaper solutions to this than replacing the mid section worth ~$600 in parts alone. Here are some pictures of my exhaust before and after repair:

http://1drv.ms/1hkRoRa