Possible Exhaust Problem on a 2000 Ford Expedition 5.4 L V8

We are experiencing a problem on our 2000 Expedition with the 5.4 L Triton V8 engine. We know that it is on the right side of the engine, and that it is somewhere near the exhaust manifold, because of the rough sound it makes---almost like a slow machine gun.
First experience with the problem came quite suddenly, transitioning from the smooth sound that this engine has when properly functioning to a machine-gun like rumble. Leaking carbon monoxide started filling up the cabin, and we haven't driven it to speak of since then.
At first, we believed it was the manifold gaskets, because of a carbon build up around the rear-most cylinder on the right, so we replaced those gaskets. However, nothing in the tone or the way the vehicle runs has changed, so we're unsure as to what the problem actually is.
The smoke seen near the right exhaust manifold is from the burning penetrating oil that we sprayed on in the process of removing the manifold for replacement of the gaskets.
Any help or suggestions on what the problem might be would be appreciated.
Update: After a day of research, we figured out that the truck had blown a spark plug up through its coil pack, thus we were leaking fuel out of the head.
If you have similar problems on your 5.4 L Triton, you may have blown a spark plug. We hope this helps. Thanks

[@matthewcarlisle8106]

Check the hose behind intake

[@mikelovesspeed1315]

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