2004 Chrysler Pacifica knocking in top end

there is no code P045 so it may be the wrong one given the 303 is a misfire in cyl3 so if you hear a noise then pull the valve cover and inspect for some type of damage like a cam or follower problem the last code is a fuel sender type problem which can be either stuck or if gas tank was hit with something the level gauge may be stuck in place.

what is the purpose of the knock sensor. will it cause a knocking sound under the intake is there anyway to test a knock sensor

if the knock sensor picks up a knocking noise it retards the spark thinking that it's preignition or detonation. But I think there is another problem other than a knock sensor from your description of the noise. there is a way to test them but I forget because you normally test from the sensor to pcm and if that stuff is ok you just replace the sensor. It has piezo electric and it goes by vibrations.