I also had a vibrating exhaust when I went to a flowmaster with dual outlets. I ended up removing one of the sheilds and tightning the others. I also turned the dampning weight by loosening the clamp. The weight was at the 9 o'clock position looking at it from back to front of vehicle. The weight is at the 11 o'clock position now. I don't know which one of these did the trick, but I no longer have the noise. Hope this helps.

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99 f150 s/c 5.4 sport pkg

 

I have a 2000 F-150 with a 4.6L V8, with about 1500 miles on it. Since I bought the truck I have noticed an uneven vibration when ideling that becomes more pronounced when the engine is warm. The dealer has told me that it is the exhaust system that is causing the vibration, and that seems right as the engine does seem to idle smoothly and run smoothly. I also took the truck to a performance exhaust place and they also sais it was probably the exhaust system. Additionally, they noticed a clamp that looked funny to them and thought the dampening weight looked to small. Has anyone else had this same problem and do you have a solution. My dealership doesn't and Ford who is aware of the problem doesn't either.
thanks

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Dburton