Exhaust leak that has become a mystery to locate

[Excelsior]

My 02 ssei has an audible exhaust leak and we've replaced the manifolds, their gaskets, the egr, the down pipe and the catalytic converter. Is there anything else that can cause an audible leak? You can hear it clearly from the drivers seat when it gets over 1500 rpm. My friends shop has been looking for the leak for two days. Smoke test yielded nothing and the two man wet towel trick didn't either. I wonder if there is just a leak or hole in between the engine bay and the cabin near the emergency brake pedal. Any help is appreciated. Thanks

[harofreak00]

When you say EGR, do you mean the valve or the tubes as well?

[ChibiBlackSheep]

On W-bodies, the resonator heat shield traps water and the seam is known to pop there.

Could it be as far down as that?

[Excelsior]

So they found a crack around one of the welds on the rear manifold and we replaced the manifold. When he was reconnecting the EGR tube, the flange on it screwed up and caused a serious leak there. Luckily, warpfactor15 had an EGR cap. We capped it off and that sealed any leaks we could further find. Unfortunately, the sound is STILL there. We are going to put in Warpfactor15's old downpipe and cat on wednesday, but neither of us thinks that will get rid of the sound. What we are looking for is other possible causes of the sound that are not normal.

I think there is some sort of hole between the engine bay and the pedal area, allowing sound to come through. Any other shots in the dark we can look into?

[Excelsior]

This car has a 4 inch crack on the top driver side side of the transmission casing. It was jb welded by the previous owner. I was never told about it. I found it when changing the EGR a while ago. Could a crack in the casing lead to a noise audible inside the car that sounds similar to an exhaust leak?

[Excelsior]

turns out the Flex pipe I had replaced my original with had a leak as well. I put in a new flex pipe today and the leak is gone!

[buickman104]

Yay! Congrats on solving your issue!

[Excelsior]

And the leak is back. I guess the flexpipe I put in failed, or a bolt on the plate failed. I don't know yet. I drove it work in the morning and all was well. I started the car to go home that night and the leak was back.

[Excelsior]

Ok, so I've just replaced pretty much everything. I put in a front ZZP exhaust manifold, replaced the crossover pipe from one from Haro, replaced the rear exhaust manifold from another 2002 SSEI off ebay, the gaskets on the manifolds are less than a year old, a new downpipe gasket, and a ZZP 3inch downpipe with cat stainless. My EGR is still capped off. Overall sound of the leak is decreased, but it's still there. Oh and I replaced the transmission with a 75k one off another 2002 SSEI.

I'm thinking that there is no exhaust leak, but a sound isolation problem. General engine noise is louder in my car than my friends, and he has a smaller pulley, ZZP exhaust like me, and more mods. The sound is coming in through the driver footwell area. Is there anything that could lead to engine noise leaking in through there? I recently found out that my car was in a front end accident before I owned it. What's weird is there is no sign of frame damage, but the transmission was cracked, and when they took the trans out to patch the hole, they didn't put the rear diff bracket back in. That trans is gone and I got a replacement rear diff mount from Haro.

Any thoughts on how to go about this? It sounds like an exhaust leak. It get's significantly louder when I get to 3k rpm and higher.