I have a 2004 ford expedition 5.4l with 217k miles that has a loud knock at high rpms and as soon as i start the vehicle. This problem occurs in all gears including park and neutral. As soon as I give the vehicle gas and rev the engine I hear this consistent knock that speeds up with the RPMs of the vehicle it seems like. Also seems like the loud knock is coming from under the vehicle and between the transmission and the motor but at the same time when I put a flat head screwdriver on the valve cover on the passenger side, I hear the same knock at high RPMs. I don't know if it's just vibrating through the motor or what. Also on a side note I have lost all oil pressure. You can watch the video i took of it and hear it for yourself the link is below, let me know what yall think. Thanks!

 

my bet is when you remove the transmission, you will find the flex plate broken in two pieces rite at the crank flange where it bolts to the crank.
i bought an 04 F350 for $500 because it had a "bad rod knock"
when i went to pick it up, i started it to load on the trailer, sounded just like that, and told the guy it was a broken flex plate.
6 hours later it was fixed with a good flex plate in it.