What can cause my car to knock?

I have an AMC 4.2 inline 6 2bbl. i just replaced the lifters, pushrods, and arms. Checked every cylinder wall for clues of wear and it was all good. old lifters had no signes of damage from the cam, so i figured the cam is fine. then unplugged the spark from the cylinder one by one and still knocks so its not a piston slap. droped the oil pan the bearings are fine no metal shavings in pan i ran a magnet threw it. the knock is preaty loud coming from the back top left of the engine it sounds almost hallow as if like you get a pot and bang a spoon in it but with a very low pich bang. the knock quiets down when the car is put into drive. heres a video as well http://www.pennysaverusa.com/info/showinfo.aspx?id=e000515695 what other tests can i run i need some edvice. thank you.