I have spent the last two nights replacing the exhaust manifold gaskets on the right side of my truck only to find that wasnt the problem. I just developed the problem after pulling my new camper for the last couple weekends. It sounds just like the doughnut is out of the passenger side exhaust manifold. I start it up and there is a terrible sounding (what I think is some sort of exhaust leak) coming from the passenger side engine or down below, then it seems to get less as it warms up.... I changed the exhaust manifold gaskets because I thought that is what it was. The local parts store says there isnt a doughnut between the exhaust and the manifold so I am at a loss for words or thoughts. I am ready to back it out of the garage and lite a match to it. I cant stand the sound of it any longer... Any advise as to what it is would be greatly appreciated...