Car making knocking noise
 

Hello, I have a 2007 suzuki xl-7 3.6l v6. This car is making a knocking noise. But not when parked and idle. But when driving or revving it while in idle then it starts making the knocking sound. Just wanted to know what could be the cause of the knocking and why it doesn't do it at idle but only when revving the engine. it does seem to lose power or try and die when giving it gas. Was thinking dirty air box because it has oil in it. I did a leakdown test and alot of my cylinders are good just the first one i had quite bit of air coming from the intake.