exhaust rattle

[amx1pxp]

Got a little problem with my car that can't seem to figure out. Hopefully one of you guys may have a clue... Anyway, 2012 9C1 6.0. AFM is still active. Car has a strange rumbling noise coming from the exhaust (I believe). It comes in just above idle, around 1100 rpm. It only is noticeable at that one particular engine speed, around 1100 give or take. Whenever passing through that rpm, whether accelerating or decelerating, it's noticeable. Sounds like there is an empty beer can or something rattling around in there. BTW, car still has stock exhaust, with the exception of SS mufflers. I've actually replaced the entire exhaust (with another 9C1 system from a wrecked car) with no change, sound still there. Could this be one of the forward cats self destructing internally? Anything to do with AFM? I know there are some pretty sharp dudes on this forum, can't wait to hear your feedback (also removed mid muffler and resonators, before putting back to stock - no change)

Thanks in advance,

Paul from Castro Valley

[Fudgehog]

The only rattling sound I've experienced in my time with exhaust work was indeed a failing catalytic converter. The screen inside and the internals had either rotted out or broken off and it was like a straight chamber.

Sounded like crap and made a sound similar to what you're describing.

[CrashTestDummy]

You replaced the entire exhaust, or replaced the entire exhaust except for the front cats? If you didn't replace the front cats, definitely drop them and look down inside to make sure you haven't melted/broken the matrix inside the cat.

Since you've replaced at least some of the exhaust, make sure the O2 sensor plugs are tied down. A loose one can bang against heat shields at certain RPM ranges.

If you have indeed replaced the entire exhaust, from manifold to tail pipe, I'd start looking elsewhere. Make sure you don't have a failed motor mount. The factory mounts are known to fail more often than they should, and you could be getting some resonance from one of them if they've collapsed. If they look good, you may want to make sure the bolts between the converter and flex plate haven't some loose, or that you have a cracked flex plate.

[amx1pxp]

I'll check the items you mentioned. Thank you both.

[Sanford]

I have a 2013 that made noise around the converter area. It seemed to be worse when it was cold. You could push up on the pipe right behind the converter and the noise would go away. I took the car in for the fuel pump recall, which required the exhaust to be dropped. After I got it back, the noise was gone. Apparently the pipe to converter connection was bolted up a little different.

David