This is probably something you don't want to hear, but I'd suggest pulling the side cover and looking at the position of the lifters where they enter the block above the cam. If the lifters at the noisy cylinder(s) are dropping lower in the block with the valve closed, you might be dealing with a worn cam lobe. You can also get an eyeball guess at whether all the lifter plungers are compressed the same distance below the snap ring that keeps the plunger from escaping in case the lifter tops out for some reason. Normally, the plunger should be compressed about 1/16" below the snap ring with the valve seated.
I prefer to adjust hydraulic lifters with the engine stopped. It's MUCH easier to get an accurate adjustment that way. PM me if you want, and I'll send detailed instructions on a non-running adjustment. I'm tired of the experts on the open forum telling me I don't know what I'm talking about.
Jerry
