Yeah, I am one of the "other 3 posts" about this. I can hear a "leaking" or "hissing" sound from the passenger side of the engine (under the hood) too. Just can't locate it.
If you figure anything out, please post it, and I will do the same. I may try to just tighten down the manifold a little to see if that helps. If so, it will be new gaskets for me...
Oh, I used carb cleaner like crazy yesterday trying to find it with no luck, but the manifold gaskets aren't the easiest to spray completely around as the manifold itself is a bit in the way.