tapping noise in jeep 4.7L engine?

[The Rock]

i own a 2000 jeep cherokee limited and it has a tapping noise in the engine,pretty sure it's in the top part.it also has a smell of gasoline in the air filter compartment.it still has good oil pressure,i know when i start it,it revs up kinda fast but then settles back down. i was just wondering if anyone had this happen before or if someone might have a clue what this could be...thanks for any help