The first thing u should do is check ur oil for any traces of coolant and ur coolant for traces of oil that will tell u if u have a head/intake gasket problem because sluggishness is a symptom of that. the car might tick a bit on a cold start before it warms up make sure ur oils full. if its just a faint not mettalic noise after it settles down its prob just the normal noise of ur fuel injectors working. another issue could be the butterflys in the variable intake manifold not working proporly and starving ur motor for air causing the knock. thats just a theory tho im not very knowledgeable on how that particular manifold works. is the sound very loud does it make u cringe? does it idle rough?