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I've had the Fabspeed Cat Bypass pipes on my 04 Cayenne TT for over a year. About a month ago, I started hearing a "thumping" noise from the driver's side of the engine compartment near my feet at heavy throttle imputs. At first, I thought it was one or more of the cylinder's missing due to a bad ignitor. It sounded similar when the ignitors went before and the cylinder's were missing.

I had it in to the dealer and they said all cylinders are fireing with no issue and that the aftermarket pipes i installed were hitting the frame when the drivetrain was under load. Mostly due to the aftermarket pipes not having a third support like the factory pre-cat-pipes.

Has anyone heard of this? If it is, why did it just start. My only guess is that the engine mounts are now getting more worn and allowing more movement of the engine. I have been down-shifting a lot more since I removed the exhaust about five months ago.

Any suggestions??? Thank you in advance.


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I would say its possible. IMO, its a bad design with the cat bypass pipes not having that exhaust mount. So the pipes just hang there and they tend to vibrate a lot. If you look under the car with the engine running you can see them and they move a lot. I've never seen them actually move enough to hit the body though. I would guess they checked all the other exhaust mounts but that would be something to check for sure. It seems like the Cayenne motor mounts have been problem free so far but you could check the torque support mount which is on top of the engine on the passenger side. Also maybe check the lower control arm bushings and the rear cardan shaft bearing.

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Thanks for reply PTEC. I will take a look again myself. I'm not 100% confident in the dealer's assessment. You made me laugh....I just replaced the cardan shaft bearing a few months ago and the lower control arm bushing last week. It's funny how we all have the same problems. It'd be nice to have a consolidated "Here's the things you're going to have to replace" list. I keep having things go and then find out "Yes, that's a problem area for the Cayenne". But, I still love the vehicle!!! It does so much.....Snow, Rain, Comfort, Speed, Looks!!

Again, thank you.


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