Engine rattle makes my Explorer sound like a diesel

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A year ago I had the upper and lower intake, the plenum and head gaskets replaced. There was a slight rattle and was told it was a heat shield on my exhaust close to the manifold that had a broken weld and was rattling,I already knew this to be true I had found it doing an oil change. The mechanic removed the heat shield hence removing the rattle only there is one huge problem the rattle didn't go away but got worse. It is so loud now that my V6 sounds like a diesel while idling and even worse when accelerating, HELP!