Exhaust manifold is welded to a plate that bolts onto the catalytic converter. That weld finally broke. Corrosion under the weld tells me that this has been going on for a while which fits with with what I have been hearing as I am driving. The truck is not under warranty and it was repaired at a Nissan dealership in Baton Rouge. I have pressured them several times to tell me exactly how this piece failed but have yet to get a good answer.