Can you remove the heat shield and look at #4? Thats where the cracks happen 90% of the time. A new manifold kit OEM from Aaron is just under $200 shipped.
This is what my #4 looked like cracked... mine wasnt all the way through yet, but I replaced it anyway. Yours sounds like its cracked all the way through but I would think your car would be audibly much louder along with the exhaust leakage.
