Today I got the car out and here is what I found; I can get it to make the knock at around 1500-2000 rpm in park when the car is fully heated up. My buddy who races Chevys put a screwdriver on the valve cover and said it was valvetrain. I listened also, it is loudest at the front of the drivers side valve cover. Put the screwdriver on the front of the block, much less noise. If I let the car cool for twenty minutes, it goes away, then returns when the car gets hot. By hot I mean heat soaked, because I don't let the car get over 180. I had to drive the car for 20 minutes or so in town to get it this warm. If you give it more gas, it goes away, like rod bearings. It is more of a loud tap than a knock. What could this be? I still haven't had the oil filter cut to look for metal, so I'm not ruling out bearings, but I do have a new 210 billet roller that was put in on the last rebuild. What could change when its warm vs. cold in the valvetrain? Lifter preload was 60 thousanths, I was told, and rocker shafts were tight last I checked. This tap is loud enough to peg my caspers knock guage. Ideas?