You need to check the leakdown rate on the noisy lifter. Get the engine up to normal operating temperature, then stop it and remove the valve cover. Tap the starter until the valve is fully closed. One good way to determine this is to watch the other valve on that cylinder- - - - -when it's somewhere near all the way open, the noisy one should be on the base circle of the cam. Use a long screwdriver or a pry bar under the rocker shaft to put a firm, steady pressure on the pushrod end of the rocker arm, and see how long it takes to bleed the lifter down to its full-compressed position. Anything less than 30-45 seconds to make the lifter bottom out means you've got a leaky check valve in that lifter. Engine-running adjustment of hydraulic lifters almost always results in an incorrect adjustment, because the lifter never gets to top out all the way. With the engine up to normal temperature, and the cylinder in question at top dead center on the compression stroke (distributor rotor pointed toward that cylinder's plug wire) back off the adjustment until there's a noticeable looseness, then wait 1-2 minutes. Then carefully tighten the adjuster to eliminate any slack and go 3/4-1 turn tighter and lock the adjuster down. If the lifter still rattles, replace it.
Jerry
