2006 dodge charger r/t

my charger has been making an awful noise under the hood. The best way for me to explain it, is it sounds like a stock car or bad muffler in the engine. When you accelerate, it gets much worse. Well, I know for a fact that its not the muffler, because its localized under the semi cover under the hood. Then, when you turn off the engine, it kind of sputters and shakes and clicks a couple times. Hoping you can help me with a possible idea of what you might think that could possibly be. Its very abnormal, and would just like some advice. Thank you
Jane Beers