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So I just installed my JTR shorty header for my 2005 3.5. While taking off the old exhaist manifold, I noticed that either the dealership that changed my head years back or from the factory that 4 of the 9 bolts that hold the header on were broken off. Now I never had any issues, so I decided to go ahead with the install anyway. So, after everything was tightened up and finished I started her up and no exhaust leaks and I thought I was good to go.

I did noticed as I was installing the header that the gaskets I used appeared to not fit in place when I let them hang on the new studs that I decided to switch to. As I was driving down the street I floored it to see what kind of gains I would feel and I heard what sounded something like a horn noise. I doesn't sound like an exhaust leak in any way. It reminds me of when you hold a piece of paper on two ends and try blowing down the thin side to get it to whistle/make a noise.

So my questions is, could this noise be the gasket hanging in the flow of the exhaust. Only when I gun it does it make that loud shrill horn noise.
 

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If it wasn't making that noise prior to replacing the maniforld, it is most likely from a leak. A lot of mechanics are not used to working on aluminum engines and don't realize that the fastener torques are much less than on iron blocks. Many reports of sheared bolts. The fasteners on the 3.5 exhaust manifold are supposed to be torqued in sequence from the center out. The Service Manual torque requirement for the exhaust manifold is a mere 15 ft/lbs (180 in/lbs).
 
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