odd 4.7 engine knock

I have a 99 jeep grand cherokee with a 4.7 v8. i have an engine knock or "beat" noise that is best heard in the interior. Its not a tick. it doesnt sound like metal on metal. When you start the jeep the oil pressure goes to 40 psi like it should and has no noise, when it gets to operating temp the gauge starts to read low and the knock becomes audible, when you pop the hood you can barely hear but can hear it loudly from the interior. the knock goes away under acceleration. i have checked flex plate and torque convertor bolts, replaced oil filter, seafoamed it, tuneup. its not a rod or main bearing and the jeep runs smooth and hasnt lost any power. when you pop the hood and place you hand on top of the breather box you can feel everytime it knocks. i dont think its a dropped valve seat because the tone of the knock and like i said it runs and idles smooth