[71 GMCDRVR]

I recently had the same sound I thought it was valve lash but after resetting the valves a number of times it just got worse. pull your intake manifold and pull out your lifters and check em. if they are damaged you lost or are in the process of losing your cam. This is what was wrong with mine! Is the sound coming from the top end? rubber hose works great for finding these noises!!...................But make sure the lifters go back exactly as they came out, I might be preaching to the choir but I had to say it that's how I roached the cam